My brother took his 02 4cyl tj mudding to realize the gas cap was missing. Now the jeep has a loss of power while going down the road, doesn't wanna rev up quick or high while in gear. I drove it and turned to go up hill and in 1st gear it wouldn't rev past 3k and just felt like it didn't wanna go. In neutral the jeep revs up fine. Any help would be greatly appreciated