Crazy throttle question

[HSRACER]

So I have a crazy throttle question for the group.

I have a 5.3 in a 67 stepside that came out of a 03 suburban with drive by wire. The problem that I am having is the transmission downshifts at very light pedal pressure and slight movement from the idle position.

It drives well when you give it slight pedal movement, but when driving it what I would call normal it always downshifts way to early.

After so diagnosis I have found the tps reads 100% at half the pedal stroke. I then pulled elbow off the throttle body and verified the actual throttle plate is wide open at half throttle on my pedal.

My question is can the pedal be calibrated to the throttle plate somehow? I would like to see it work with half pedal equaling half open throttle plate and so on. if it can be done is there a sequence or procedure that you can share with me.

I am just learning the whole LS drive by wire thing and have a friend who is just learning the HP tuner program. We are novices at this kind of diagnosis and repair so be gentle!

Thanks for any assistance you can give.