I have a problem with my car?

I have a problem with my car… It is a 97' Ford Mustang and my Overdrive keeps turning on when I turn it off it turns back on in a minute and this cause my RPM on the freeway to be VERY high and it doesn't go down the whole time I'm on the freeway how can I fix this?

With overdrive ON - Your transmission will shift into 4th gear at cruising speed. The O/D light will be OFF. Engine RPM is lower.

With overdrive OFF - Your transmission will NOT shift into 4th gear at cruising speed. The O/D light will be ON. Engine RPM is higher (because it stays in 3rd gear and doesn't upshift into 4th).

The problem you're describing is that your Overdrive (4th gear) is disengaging or failing to engage at speed. What that means is the transmission is staying in 3rd gear when it should be in 4th (which would explain the higher RPM you're seeing). Your overdrive is not "turning on" when the RPM increases - the O/D light is turning on to tell you that your transmission is NOT in 4th gear (overdrive) and it's probably telling you there's a problem that's causing it to stay in 3rd gear (where the RPM will be higher, which you are describing).

My guess is that you've either got a transmission controller problem or a sensor problem that's causing the controller to shift out of 4th (overdrive) or just stay in 3rd while cruising. There's really no home-remedy fix for this sort of problem - it's time to let an expert take a look and diagnose the exact cause.

If the overdrive came on, the RPMs would go down. Are you trying to confuse us?

The O/D light tells you when it is OFF. When the light is ON your Overdrive is OFF. And vice versa. It sounds like your transmission controller may be the issue. Your TPS could be bad making the transmission think you're at WOT and shift into passing gear. Or you're doing this backwards and everything is fine.