I also have an HP Tune with supercharger, 4.30 gears (stock), I have run 35s and currently have 34s.
You say funny when shifting from 2 to 1. Does it shift hard? Does it hesitate? Does it gently slide into first? Or is it down shifting as you slow down and you notice it now with the HP tune? With the stock tune the truck does not down shift attempting to slow you down as if you were in sport mode and had down shifted manually. With the HP tune it will do this. I only notice it in 3-2-1. It will also do this in the other gears on long down hill grades attempting to maintain a speed but I am usually shifting at that point and don't wait for the computer. Most older type auto transmissions just coast down hills. The newer designed trucks of the big 3 will all attempt to hold a speed by down shifting automatically. You can see demonstrations of this on TFL Trucks when they are testing on the IKE gauntlet. They test the trucks ability to hold a down hill speed.
With the HP tune the torque converter locks and un-locks rapidly and will down shift rapidly with any slight input from your right foot. This is completely un-like the stock Toyota tune that is always trying to keep the RPMs at 1200 and only allowing a downshift when you get the throttle half way to the floor before anything happens. All modern Toyota's I have driven perform (or should I say don't perform) this way.
Hope this helps.
