Just picked my truck up from the shop. 03' 2500HD ECSB 4x4 6" lift, 35's w/ ProCharged 6.0L. I had the gears swapped from 4.10 to 4.88. In the short drive back to work (about 5 miles) I have to say the s.o.t.p. difference is hardly dramatic. The MPH gauge flies to 60 now but that's just cuz I need to calibrate the PCM still (at 60 speedo I am only going 48gps), got a service brakes code (calibration problems I am sure). From a dead stop hammering the throttle doesn't really feel any different, still no chance of breaking the 325's loose (I guess cuz it's just a huge, heavy *** sob) once the boost kicks in it feels a little better than before. I am just glad I went two sizes up, I think I would have been really dissapointed w/ 4.56's. Haven't gotten on the freeway yet but expect cruising rpms at 65 to be in the 2500rpm range. I can't say I am happy or dissapointed yet cuz I havn't really had more than 10 minutes in the truck yet but I guess I expected a very dramatic change for $1700, a 20% change in gearing seems like it should have had a big effect. Oh well, tomorrow the PCM comes out for a recal, and the 43lb injectors go in as well (so I can ditch the FMU), so I guess I'll find out next week, how the thing really runs.

 

I was never too impressed with gear swaps. Just never had good enough results to warrant the gas milage change or price

 

Damn that sucks....sorry to hear you didn't gain that much. I guess its because your trucks a 2500 HD and weighs a good deal more, but i break loose my 35x12.50's from a dead stop for about 5 or 6 feet without powerbraking with just a 4.56...and i've only got a 5.3 with bolt on's. And it is noticeably faster than it was stock even with the heavy *** wheel's and tires...(102 lbs each). Im probably going to step up to 5.13's when i swap out my rear and go up to 36's though.....i was happy with the gear change and IMO its worth the money.

 

I guess I should give it a fair chance, 10 minutes in stop and go traffic and only one off the line jolt isn't really enough to have a real opinion . Really my main concern was towing ability before perfomance, I yank my boat around alot and just bought an 8,000lb travel trailer too, if the gears help even a little to relieve some stress on the tranny it'll be worth it, any performance gains will be a bonus. If I didn't have to tow I would be looking into stalls more, I think that would really wake up the off the line performance.

The guys at the shop were the ones that talked me into the 4.88's over the 4.56's they said in a manual tranny the gear changes are much more noticable but since I have an auto I would need to go at least two sizes lower to really notice any change, it seems they were right. Gas milage is not an issue, it has sucked since I bought the truck, I have averaged less than 10mpg since new.

 

Ya there pretty much right about the auto/manual thing and noticing gear changes, but a manual will respond better SOTP to anything over an auto just because of effeciency. I know the feeling on gas mileage, i only avg about 10 mpg as well city and only 14 on the interstate. Give it a little more time, a gear change is well worth the money especially if you tow or your hauling alot more wieght. In our case, rotational weight is the enemy

 

A ECM upgrade to new gear ratios is a must as you discovered as ABS will not work either until you do. Check out how much better it pull OD now though.

 

My abs didn't work regardless even after reprogramming, but i also think my rear gear set didnt have a reluctor ring on it.

 

GM does not use one in diff but ford does.

 

[QUOTE=LS1S10]A ECM upgrade to new gear ratios is a must as you discovered as ABS will not work either until you do. Check out how much better it pull OD now though.QUOTE]

I had trouble with the ABS after lifting it originally, so this is not a surprise at all the PCM recal took care of it last time too.

 

I thought our trucks used one like the late model f-bodies did...but i went out and looked and theres not a plug on the diff so i guess not. Oh well, i just put some black tape over those pesky lights under the overlay. ABS is a good thing to have, but it makes it even harder to stop when your rolling on big rubber. Mine works for about the first 5 miles i drive and then it goes off when the lights on the dash come on. Doesn't pull up any codes so i dont have a clue what it could be.