My truck has been acting erratically lately when cruising on the highway. The RPM's stay around 3000 when driving at 70MPH and as soon as I let off the gas it quickly drops down to about 75ORPM. Then when I get back on it again it has to jump back up to maintain speed. I've already replaced the TPS and I just replaced the overdrive solenoid & pressure sensor when I changed the transmission fluid this weekend. Is there a fuse or relay that's gone bad - if so where is it. It seems like it's shifting into 4th, but if I continue to speed up past 70 the RPM's continue to climb. I didn't want to start screwing with the bands this weekend either. Also when I push the O/D Off Button at 70MPH (although the light comes on) there's little or no change.

Any help would be appreciated b/c I'm puzzled.

 

That doesn't make sense. If you are going 70mph and your RPMs drop to 750, I would think you would stall out. 750 RPMs is idle. You couldn't keep highway speeds at such low RPMs. If you were in O/D your RPMs would be 1500 to 2000, it's obviously not engaging. Your O/D may be off or a sensor is giving bad information, or both.