94 Z28 Gremlins

Hey All: Been a lurker here for some time and usually found answers to problems with a good search.(Thanx 2U All!)
This is my sons car and the problem is with the shifting and the Speedo.
LT1 w/4L60E. The first shifting problem turned out to be the TPSensor. The thing was slamming all gears and sometimes wouldn't shift out of 2nd.
NOW the thing acts normally 95% of the time but then throws a fit where the Speedo quits working and it won't shift past 2nd(again). I put a new speedo sensor in the tranny, he picked it up and three days ran perfect. He called me tonite and said it's doing the same thing again. DOH! Sometimes when he shuts it down and restarts it, it returns to normal for awhile again.
I wonder if I'm fighting with a dizzy ECU. :banghead:
What you guys think?
I have another ECU that I can try but will have to get it flashed, (whatever the hell that means). Is this worth a try?
He did put .373's in and used a Hypertech scanner to only adjust the speedo to read right, but that was some time ago with no problems then.

Thanx All !
(Wild)Bill

Could be a bad eprom (especially if it has been flashed with a hypertech). I would first check the connection and wires to the VSS , then scan the PCM for trouble codes and then try to swap pcm's. Good luck.

John