I have a 2001 Ford Ranger XLT 3.0 Automatic. A few days ago it started downshifting hard and any time it is over 2 RPM it revs up and jumps to 4 RPM out of nowhere. It only drops when I take my foot off the gas. It seems like it is randomly accelerating. Changed out the Throttle Position Sensor and still no luck. I am nervous to drive it and could use some help! Thank you!

 

that sounds like a failing torque converter

the pcm controls the converter lockup , torque converters do fail

how does your ATF fluid look like , if it is brown or near black in colour , that is a sure sign

 

Yes ^^^

I assume your speed doesn't go up when this happen, just the RPMs

If your foot is on the gas pedal and you are going 50MPH at 2,000rpms and the load on the engine is released(torque converter unlocks) then engine RPMs would easily go up to 4,000rpms with foot on the gas pedal in the same position.
This would be a transmission issue.

If your speed was going up and down with RPM without gas pedal position change that would be an engine issue.