Ok guys, I have a 1989 Ford Ranger XLT. It's a 2.9L with an automatic transmission. Every once in awhile, When driving on a fairly level road my truck would drop a gear and the revs would jumps to about 2700 or something like that. For reference, the gear change is somewhere between 53-60 mph and it settles at 2000 rpm. What I would usually do would just floor it for a few seconds, jump the rpm's and it would settle back down. But on my latest drive, it wouldn't stop. It would settle down but then it would jump around 3-4 times dropping a gear and hiking the rpms. This went on for about an hour. But when I finally go to my destination, I found that I had no radiator coolant. Would dropping gears and hiking the rpms be caused by overheating? Please help!