Engine Performance problem
1997 Jeep TJ 4 cyl Four Wheel Drive Manual 165000 miles
i have a 97 jeep with the 4cly and when im on the freeway it is hard to get up to 70-75 and when ever I go up a smalll hill or go over an over pass I can not maintain speed, if im going 70 I will slow down to about 63-65 and if by chance I am doing 75 then I slow down to about 60. I had the cat checked and that was fine but they found a very small crack in the header. I have checked the plug gap, wires, and cap and rotor and air filter and replace them all. Where should I think about checking next? People thell me that its just because its a 4 cly jeep but other people that have 4cly jeeps say that they dont have this problem!