A friend of mine has a 91 with an auto trans in it. The truck runs great and is super clean, however the trans is acting strange. The trans shifts well and seems strong but does not seem to want to stay in overdrive. The trans shifts in and out of overdrive when traveling at a steady speed. I know the vss can do this but I believe his is working fine. Any solutions or troubleshooting suggestions would be greatly appreciated. I don't know much about and auto.

 

Check and clean the TPS. There is a certain point on the TPS that will cause it to keep kicking in and out of OD at a steady speed. Follow the write up in the sticky and I'm sure that will fix his problem.