i have a 94 z-28 and my car is automatic and when it shifts it like throws me into gear like when it shifts it jolts ya back in your seat and the other day i stepped on it at the start and it squacked in second gear a little and i was wondering if all do that or if it might have had a shift kit in it my friend tells me it seems like it might and i know the car has had performance parts cause i have a lingenfelter throttle body so if someone can answer ...

 

squacked.
Love that word.

It might have a shift kit in it.
Or it might have programming that upped the line pressure.
both of these will make the tranny shift harder.
Only way to know for sure if it has a shift kit is to open up the trans.
I would just drive and enjoy it.