Been a little disappointed with the low end performance and highway mpg on my truck. Its even downshifted going up mild hills on some road trips. There is no reason that should happen in my opinion. 375ft lbs and an unloaded truck. I average 14.8 in town and have taken a few road trips in the truck's 5800 miles. Most highway trips were in the low 16 range with a best ever of 17.1 previous to today and DOD never comes on at highway speeds unless I decelerate. Looking at the factory tune, the timing values are low all over the place and especially low in the cruising zones. In fact, many cruising cells have negative timing. IMO, there is no reason for this other than transmission protection.

350 mile (one way) trip on Monday, 50 degree temps, no traffic, no wind. 16.2 mpg average.

I removed all negative values from both the hi and lo octane tables (just tuned them to be zero) and cut the IAT and ECT timing adjustments by half.

350 miles back home today. 70 degree temps, 20 miles stop and go, 10mph head wind. 17.5 mpg average. Very rarely saw DOD come on outside of deceleration.

Im sure there is even more to be had once I spend a while on the timing tables.

This seems to help the hesitation when you romp on it as well, but doesn't completely cure it.

Just wanted to post some real world results. I will try and post more as I iron it out.

 

man, thats why i love my truck so much..
i can get 22 on the highway and 15-16 in town. and i have a LQ4 and 80E with a STS kit..

With the 65E in there it never dropped out of OD nor did the converter ever unlock when hittin steep hills towing a 89 Camaro to the track or a 96 Cobra home... i know the Turbo helps in that area.. but even with the 5.3 in there it was nice... the new trucks are so sophicticated in the ECM, TCM its not funny..

 

Your mileage seems pretty low compared to mine but I am at higher elevation so engine gets less air so less fuel and of course also less power (I'm at 3500 feet). Also most of my driving is in town and our speeds are perfect for DOD (40-50mph) and truck will cruise along in V4 for quite a while...we have a fair amount of longer roads and I usually do about 8-10 above posted, cops are insane up here with the money makers (radar) so I get about 20 in town and about 22-23 on the highway. Some people have called BS on these numbers but I have double checked and thats what it is (interestingly enough, my 97 RCSB was about 16-17 in the city and about 22-24 on the highway with a 5.7/3.42 gears/15" wheels).

These trucks push a lot of air and are heavy. My 97 was about 4100lbs (weighed), this one is probably close to 4600lbs. Plan on weighing it this weekend actually. Your truck will be that much more due to crewcab.

I too have HPTuners and have been playing some. My goal was to get it to stay in V4 at highway cruising speeds for mileage, but its tough. Might be just too much air to push for it to work, but I did get it to stay on longer with more TPS allowed, played with vacuum enable/disable charts and a bit of timing. I didn't buy the software for tuning mileage, but hey why not play, right?? Bottom end you could up the torque allowed on the traction control so its not so intrusive, or disable it altogether. I ditched 50% of my torque management and it helped but its still pulling timing from somewhere, although not as bad.

I'm a newbie at tuning so going slow and learning lots.

You do have a pretty big truck, can't expect awesome numbers out of it. Keep us posted on the tuning, its interesting to see what works and how much.

 

i played with my v4 mode a little bit and have got it to stay on during hwy driving i put the tps to 35% i get a little over 20 mpg while on hwy drivng up and down the cajon pass

 

niugnep,

You have a regular cab 5.3 while my truck is a crew cab 6.0. Its rated at 13/18 and I am plenty happy with the city mileage I have been getting. I wouldn't mind the crappy highway mileage if I felt like the engine was performing, but its not. The truck is an absolute terd under 2500 rpm and that contributes to the poor mileage. I am confident its 100% in the tuning and I will get it worked out.

I played with the DOD percentages a while back, and it would stay in DOD longer, but it would pick up knock and shake with anything over 10% TPS, so I have left it at stock for now.

 

have you tried to just remove the DOD and see if that helps?

I know it sounds odd but have you?

 

worse without DOD, especially in town. Mileage that is.

As for lack of low end, it makes a slight change since you elliminate the transition from 4 to 8, but even with DOD off cruising down the road and you hit the gas to pass someone, the timing still drops to 0 and the truck hesitates.

 

Yeah sorry I never noticed you had crewcab until I posted (thus the edit). Thats a big truck for sure, you can't have everything!

I have about 15% on the tps, seems ok. No knock or vibes, but I think the vacuum tables make more of a difference...but I think once you hit 55-60 mph or so these things are pushing so much air you can't do much about it. I wish GM had gone a little more aero on the hoods and trimmed the fat a bit, these trucks are big and weigh a lot.

 

i feel you on the low end and my mileage dropped dramatically whe i put on my 22's... like 5mpg!!!! hopefully i can some back w/ my exaust and cai that i have ordered along with a tune!

 

Took another trip today. 17.8 going, 17.9 coming back. Hot and humid, no traffic, no wind.