The tranny in my '93 Rally Van (3/4 ton) is acting up a little. It likes to go in and out of lock up in D and in OD, all speeds (30 to 65 mph).

From the bolt pattern I'm pretty sure that it is a 4L60E. Correct me if that is wrong.

My questions:

Is there a way that I can add a switch to put it in lock up always? For troubleshooting purposes.

If it were the brake switch would it also cause the Cruise Control to quit? I ask because the cruise works just fine, making me think that it may not be the brake switch.

Vacuum seems to be fine, always better than 20" Hg.

Thanks,
JP.