Now you all will probably think I'm crazy, but I've been playing with the truck one change at a time, to a ten minute run.
I've now got the truck feeling very comfortable with basically the stock setup, but 1.7 rear pistons with two additional #55 holes drilled in it. And installed 1.7 pistons up front, and the thing feels just like I was looking for.
I know above I was going to go back to the 13.5, but decided to leave the 10.5 I've started with in it and make the truck comfortable to drive. With the same motor, I feel the lap-times dropping are a result of the setup changes, rather than a motor change.
And honestly, it's not that the lap times have dropped, they've just gotten much more consistent because the truck is comfortable to drive, rather than feeling like a pucker moment waiting to happen at any corner or jump.