Need some help, I was driving my Jeep last week and everything was fine, I slowed down to about 30mph gave it some gas and the RPMs went up however the speed didn’t. Eventually it worked again, and now the Jeep is intermittent. It feels like it isn’t going from 2nd to 3rd however when you press down hard on the gas it boggs down. Then I drove it again and everything was fine, till I pulled out and stepped on the gas and the rpm’s dropped then went up then dropped and the speed didn’t change. Do you have any idea what they may be caused by?

2000 Jeep Cherokee Sport 4WD