87 L6 Auto Trans problem

Hi all,

I have an 87 L6 which sometimes doesn't shift into 4th gear. There is a transmission light that comes on warning about third gear start only and other times the light will flicker. The transmission seems to hunt back and forth between 3rd and 4th and other times it works perfectly.

I had the fluid changed and then they replaced a switch in the throttle body that cost $180.00 bucks and made no difference. It seems to be like a lose connection somewhere because of the light flickering?

Has anyone had this problem or know how the system works? The tech working on the car says he's never seen a car do this before.

Thanks in advance!

Tox!