this is going to sound mean but your 4 cyl actually had power?? LOL I have a 4 cyl and it is not powerful by any means. I have always had to downshift one and sometimes 2 gears to make it up a hill and keep speed.
So onto your question now
. So it just started happening or has it been a on going problem. Has your gas mileage been affected also? When was the last time it had a tune up (miles on the jeep now?)