2-3 shift problem
 

A couple days ago for the first time ever my car started slipping on the 2-3 shift when I would stab it up a hill or go WOT. (At the track the other day it bounced off the limiter from 2nd to 3rd) However it doesnt slip at all when driving normally. Today I went WOT a few times and it didnt slip but then later on I tested it again and it slipped. I'm not sure what my issue is, my dad thinks its because I need a tune possibly because we believe my air/fuel ratio is off and the MAF is reading wrong. Also my deceleration in 3, 2, 1 when selected by the shifter isnt existant unless you sorta rev it then the deceleration engages (this has been that way for say 2 months) and a GM tech said it was my MAF making it do that. Does anyone know what my problem is exactly?
BTW the car has 70,000 miles

I would say there are some issues with the input drum , 3-4 clutch slipping , I say this because of the downshift statement , The braking effect is caused when the overun clutch in the input drum is turned on , This is a purley mechanical function ,The reving of the engine ony serves to increase pump volume allowing the clutch to apply , There could be several reason for this , worn or damaged drum , cracked overun piston , broken or mising pump to reverse input drum washer , worn or damaged teflon rings on the input shaft , worn or damaged pump stator , pump cross leak , In anycase I would beleave it to be and internal issue ,
hope this helps though its not good news ,
performabuilt