trans slipping

hello all
I have a 90 jeep larado and I have noticed when driving around 50 or so the trans all of a sudden just slips out of overdrive and motor revs up.It has been getting worst.all i do when it happens is let off the gas pedal or push it harder to the floor and it will strighten out for awhile .did anyone have this problem ? can some one give me some ideas whats wrong?thanks in advance wayne

check the fluid level first of all. or it could be a tps

Yes, check fluid level first. If that is good, you will want to scan the values of the sensors...throttle position, output shaft speed etc.