I have been rebuilding a 1995 LT1 with auto transmission. Among a number of things, I have used a BG transmission cleaner and then changed filter and flushed entire system. Before this procedure, the transmission shifted really hard from first to second and then the other shifts were softer, smoother and normal in my book. It does not see to slip, just takes it a while to do the shift at about 2000 rpm. When I say hard shift, it tends to grap and jerk you a bit. Looking for things to check and possible causes to remedy.
Thanks in advance

 

Check your fluid level, low fluid can make it shift late and harder.

 

Hopefully you were careful not to leave any foreign material, like tiny bits of fabric from cleaning rags, as they can foul up the valve body and give all sorts of weird problems. Otherwise you may have some bad parts: like a 2-4 band apply servo, the "A" solenoid sticking, piston seal nicked worn or burred in the 1-2 accumulator.

 

A bad TPS or a PCU can cause these problems.

 

check grounds, check vss connection and wires. look for any wires that may have gotten squished.

 

did you rebuild or just flush it ,pictures I hear alot is what helps others post some pics of your build