I took my car out yesterday for the first time since early December. Before I let it sit, the TCC lockup was working fine, but now it seems at around 50+mph the lockup does not engage. It also takes a while to shift into OD, and when it does, any variation in the gas pedal will drop it down into 3rd again. I suspect that's because the converter isn't locked. What might be the issue here? How can I diagnose it?

I had installed a Corvette servo right before I put it away, but everything still worked perfectly after. I don't know if that's part of the problem, but that might be useful info.

 

3 most likely causes: pedal switch, TPS or speedometer

Check your brake pedal switch.

Use a scanner to look at your TPS and Speed as the ECM sees it when it happens. See if the ECM is commanding lock up.