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
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