It's been awhile, but this year's performance inhancements included a power programmer, and the new Y-pipe. The programmer helped me keep my speedo in line from one set of tires to the next, get rid of the speed limiter, tighten up my shifts and control when it shifts, and apparently give it a power tune that's probably good for a couple few HP.
I also removed the throttle body plate, and ground off a 1" lip on the bottom side of the plate that was designed to smooth out throttle tip in. After grinding it off, throttle response was a ton better, but I don't think I got more than a couple HP from that, but the power does come on a lot quicker.
The last thing I did was the Y-pipe, which is the biggest improvement of the year. I went from what is about 1 5/8" at it's best position, to something close to 1" where it was squashed for some reason, to a full 2", and a nice collector where both pipes were put together into a single 3" just before the cat (which is already 3"). I also removed a preconverter that apparently doesn't do much but make it quieter and slow the truck down.
Some of this had to overcome a HD hitch assembly that is permanently fixed under the rear bumper in case I need to two some stuff.
This years improvements have accounted for about .45 sec faster for the year.
Next years tentative plans are for a 4.10 gear and maybe a set of headers.
-BP