Yep thats right and a nice rear end so your problem isnt there..Have you tested the coil packs by chance.Maybe one or two is getting weak?



Side note : my blue Z71 (Bubba) has 3.42'* and a 33x12.5 tire..

the "mileage" tune would most certainly change your shift points down to short shift as normally with the stock size tires thats what you want. but you have over sized tires, i would go to to the original tire size or put the stock tune back if you dont like it. you never really hear much good about those out of the box tunes anyway most get custom tines for your truck. the other thing is did you get the computer adjusted for the different tire diameter? you could be going farther per tank than you think if the speedo is reading off.

Your tire size is equal to a 33" tire, just like mine. I looked it up to be sure too.

Since you have the 3.73s you should be fine. I'm betting when you got it "tuned" the shift points changed. Doing this actually hurt you, as it'* shifting too early and bogging you down. Try running around in "tow/haul" mode and see if that helps you any as that will raise your shift points.

I have not checked the coil packs, I dont know how to. And I dont like the out of the box tunes either, but my uncle had it and words were said about my truck running poorly and he went ahead and put it on for me. I would really love a custom tune by Blackbear or some other big name guys but I just do not have the funds nor the time to have my truck down for a week or two. I imagine you guys are spot on the money about the tune lowering the shift points and lugging my truck. And he also recalibrated the speedo to I think 32" tires because he thought 28/70/16s were actually a tad smaller than 32"*. So if I am really running 33s and the comp thinks 32s, then yes my truck is getting a tad better mileage than I think. Ive had my Garmin in my truck a few times and when the speedo on the truck says 70mph, the garmin says 71 or 72mph. Im not going back to a smaller tire, I may go bigger when I get a lift, in the future. I may not get the heavy friggin nittos or toyos again but not smaller in size. I may get federal couragias next time. Thanks to everybody giving me ideas and advice on this truck, I really do appreciate fellow Chevy people helping others!

@MouSe I will sure try this Tow/Haul mode for the next tank full or two.

nitto'* site says they are 33.03. also what presure are you running? sometimes you can run a higher pressure to increase mileage

It would depend on if he is running P or LT series tires since it comes in both.

If he'* running P series the PSI shouldn't be less than 36, and no more than 40.
If he'* running LT series the PSI shouldn't be less than 45 and no more than 65.

all the nittos on the site are lts if hes still running 35 that would be some lost mileage too.

I run them at about 40-45 psi

i think my old man is running 50fr-45rr and then 50/50 with the camper. his is a 04 ext cab short bed, he was running 50/50 but the back ones kept showing signs of over inflation. thats 265/75 lt