Redo your shift points much higher then. You have a similar setup as myself except I don't race on the bigger tires. I run around on the stock 265/75/16s which are about an inch shorter and I can still cross the traps in 2nd if you I raise the rev limiter to 6500 or so.

I highly doubt you'll ever spin those tires from a dead stop untill you do a good TQ converter and some more mods.

You have the same truck i do and I'll tell ye it was a bumpy road from 16.20@85mph to 15.0@89mph or so. From there it was a simple cam swap, tuning and weight reduction to 14.3@97mph..... Or you could just do a turbo My mods to get the low 14s were:

AS&M headers
Gutted cats
Muffler (Magnaflow)
226/.535/112 cam
TT3000
Custom tuning
Volant intake
200lb weigth reduction
Home ported TB (never noticed anything form this mod)

(Rev limit at 6800rpm. Fist gear shift at 6400rpm, 2nd gear shift at 6300rpm, I had to manually hold the shift form 2nd to 3rd till 6600rpm or so at the track once I got into the 96-97mph range)

My stock GMC polished wheels with 285/75/16 Goodyear AT/S weigh 67lbs each. The stock Silverado 5-stars with stock 265/75/16 Firestones weigh 54lbs each. Get the lightest wheel and tire combo you can if you wanna be fast and have good gas milage.

Also I never hear anything good about the Edelbrock headers on any LS1 based car/truck.

 

Well I contacted Diablosport and told him about my problem. John told me to send him the tune in my truck and he would get another one made for me at no cost. Hope this does some good and i might just keep the headers, I really dont want to send them back anyways .

 

So what did you do to go from 16.20's to 15.0's, every thing minus the cam, tuning and weight reduction?

 

play with the shift points and stuff in your tranny.

the best thing i can tell you is without a stall, i get better times stalling up to 1200 vs 1500.

on the same night, i changed my stall up from 1500 to 1200 and lost almost 2 tenths in the quarter. so i basically went from 15.0? to 14.8 and some change. just from that.

i have my predator set to shift at 5900 on the 1-2 and 5875 or so on the 2-3. i am about to install a cam and help that out so i can rev a tad higher.

when you get your tune from johan, drive on it for a while and have a passenger ride with you to log data for you since pred don't keep it. after 30 minutes or so of driving get on the interstate or whatever and do some 55 to 85 wot runs. do this several times so you can check your ltrms - they should be zero. then check the KR. if you want and can, find a spot with no traffic and do some 0 to 80 or 90 runs also. to monitor both those. i was running lean pretty bad after a custom tune and had to back down my spark advance. i hope this helps you out.

last thing, what is your elevation?

 

I live in Richlands N.C. so we are at sea level if im right. Thanks for the info What did you do with the line pressures? I remember reading something about the tow/haul button and the tranny shifts? whats the deal with that.

 

I had a Volant intake, magnaflow muffler (stock piping), gutted cats, LS1 Edit (no custom tuning, just TQ managment junk and shift points), TT3000, ported TB (homemade), no tailgate or backseat.....

In my truck I would extend the rev limiter to 6700rpm and my 1st to 2nd shift point around 6k and then hold it in 2nd gear till I crossed the traps. At stockish HP levels this was simple and although I am well out of my powerband the extra gearing made it worth it. As i made more and more power this got really hard to do and by the time I was trapping 97mph I would still bump the limiter at times in 2nd gear crossing the traps at 6600+rpm.

On my converter the biggest thing was to stall it up over 2000rpm for my best 60'. If I didn't stall it up to the point it was almost pushing me over the line then my times would drop 2 10ths or so on average.

 

i never messed with the performance settings which alter the tow haul mode. i played with the normal settings. i changed the shift speed to -22 which speeds the shifts up. at -25 the tranny clunked too much. shift firmness (line pressure) i went +23. +25 made it clunk also. keep in mind, you can set the rev limiter but there is also a speed setting. i think my speed setting for 1-2 shift is 43 or 45. i can't remember but it correlates with the rpm that i shift at. for some reason, you can't set just one.

i think what is happening with you, you are shifting way to early and falling out of your powerband. you can set the thing to 6000 and not hurt anything. personnaly, my truck feels better shifting a tad before that. also, when you get a custom tune, ask for at least 80 percent tq management taken out. you will feel a noticable difference when you punch it and downshift to first or second. there will not be that feeling of the tranny searching for a gear before it fully goes.

F8L z71 where you shifting that high with the stock valve train? that seems wickedly high! I think the pred won't allow much over 6K if i remember correctly

 

I didn't really shift much over 6400 on the stock valvetrain. I didn't really need to. The truck would almost run the 1/4 through 2nd gear stock because of the 3.73s and 31" tall tires. Once I had the cam in and started going faster I would rev it to 6600-6700 all the time but i did have Z06 springs on it and decent pushrods

 

I know that now, i can click the tow haul and when it shifts it is REAL firm. Im araid ill be having problems in the future with the tranny cause it has started to flare up on take-offs here recently.. But I guess thats why I work at a chevy dealership and why I bought all those tools :-). Can the custom tune with the predator have the TQ management removed?

 

Chevymec, yes, Johan can remove all the tq management if you wish. untill you get a transgo i would stay with 80 percent removed. When i had my stock pred tune, BigKID checked my file with autotap and we discovered that zero tq man was removed on the 1-2 shift and only a small percentage was removed on the 2-3 shift. kinda made me feel cheated since it was advertised that tq man would be removed.

if you want the normal driving experience for everyday, don't change much on the normal settings. if you want to use your tow haul button for performance then use all the settings for that. i was just worried that since the line pressure is already raised on tow haul mode that something would break if i raised them more. so i only tweaked tow haul a bit.

if you are interested in getting more mods, your tune will get better. imo! i added my pred when i only had free mods, plugs, wires, exhaust and a crappy custom intake. since then, i added the vette servo, a nice custom intake, 3.73 gears, underdrive pulley, and efans. i still have 4.10 gears to install and a vette cam. so we'll see how it goes with those.

F8L - i have 31 inch tires on my truck now. i did have 30 inchers and with 3.42 i shift into second right before the line. now i shift way before the line. with your shift points raised that high, you can go across the line in 2nd? hmm, i wonder what kinda stress that puts on the valvetrain tho. of course, as soon as i do the cam swap and gear change, all my present stuff is gonna change