Have a few Questions

[Jackpine]

You're actually the second person here who's said the TB spacer helped economy. Working on the principle that, "If it ain't broke...", I'd just leave it in place. And, if you're happy with the CAI, same goes for that. Some people really feel they help, and, who am I to disagree? I think the Gotts Mod helped me, but again, it's just my opinion based on many tanks of gas before and after the mod.

As far as the tires go - when you're in the 32" diameter bracket as OEM, every 2" bigger is going to be a 6% hit in performance (or a 6% increase in engine load, depending on how you want to look at it.) I would guess you've lost about 10% with your tire/wheel combination. The only thing that's going to really recover this is new gearing. A tune will help some, but it will continue to help with new gears too. The changes you noticed are due to the "load" seen in ordinary shifting. Part throttle shifts are based on vehicle speed (which is now wrong due to the big feet) and engine load (actually throttle position, but it indirectly equates to engine load). The load is 10% higher and the speed is probably 10% higher than is being reported to the PCM. I'd be confused, and I think the PCM is too.

I kind of look at it this way: "If you're willing to spend the money for the new feet, you really ought to spend something on the gearing too."

If you always put 91 octane in the tank, you definitely want a custom tune for that.

- Jack

[Longshot270]

If you are focusing mainly on economy, tow tunes have a tendency to get better fuel economy. They may also be beneficial in the type of driving you do. They are designed to get tires turning and keep them turning. My tow based tune gets better mileage than my performance tune because of that. It is also better behaved in crowded city driving because it isn't as jumpy due to a less aggressive throttle map. With the tow based tune my truck is actually the same speed as everyone else, just with more grunt power. The only problem is it does not have the same get up 'n go as the performance tunes until you are at upper highway speeds. If you dont usually use 91, that might be worth considering.

[PhqChevys]

Originally Posted by Longshot270

If you are focusing mainly on economy, tow tunes have a tendency to get better fuel economy. They may also be beneficial in the type of driving you do. They are designed to get tires turning and keep them turning. My tow based tune gets better mileage than my performance tune because of that. It is also better behaved in crowded city driving because it isn't as jumpy due to a less aggressive throttle map. With the tow based tune my truck is actually the same speed as everyone else, just with more grunt power. The only problem is it does not have the same get up 'n go as the performance tunes until you are at upper highway speeds. If you dont usually use 91, that might be worth considering.

Funny... my truck is exactly opposite of yours. My truck get's around 15-16 mpg in 87 performance tune and around 13-14 mpg in 87 tow tune. I asked Bill about this and he said that with the tow tune the A/F ratio is much richer to keep the cylinders cooler while under the heavy load of towing... makes since to me...

[Longshot270]

Yep, goes to show that every truck is different.

The trend is usually better mileage from a tow tune when you have a low axle ratio, bigger tires, lifts and such. There is also a throttle input difference for me as well. My tow tune has a throttle response more lethargic than stock because I had intended to use it for driving off road where I dont want a sensitive pedal. That basically gives me a smarter foot for fuel economy when on the street. It isn't as much fun as my performance tune but I'm not having to visit the gas station as much.