I drive a 91 dakota with a 42rh (hydraulic) automatic transmission. Basically this is an old torqueflight 3 speed with an overdrive clutch and lockup torque converter added. The original transmission is all hydraulic but the overdrive and the lockup converter are electronically controlled by the ECU.

The issue I have is that the overdrive will sometimes be disabled for a few days at a time. Usually after the truck sits overnight, I'll turn it on the next day and the overdrive won't work. The lockup torque converter also fails when the overdrive is off. After a day or two of this, it will start working again, along with the lockup converter. A few days later, it will go off again.
From reading the repair manuals and info online, I'm inclined to believe it's either:

1. An electrical or ECU issue.
2. A sticky lockup solenoid in the transmission

.

There is one thing that totally loses me though:

• When the overdrive is working, high RPMs cause a screeching noise from the engine. It sounds like metal on metal, sort of like a brake squeal, but a bit heavier. It does not sound like a belt noise, but might be a pulley.
• When the overdrive is NOT working, I can't get the screeching sounds to happen.

I'm pretty lost here. Can anyone help me figure out what is going on?