1999 AC / Hesitation while accelerating

Hey guys. My Cherokee is a 1999 sport, auto, 4.0, 4wd. with 90kmiles.

I have get hesitation while accelerating to enter a highway or pass someone.. It does it at about the 45 mph mark.. The harder I press the gas, the more you can feel the hesitation. If the AC is on, the hesitation is so much worse. I assume the AC is causing a much bigger load on the engine..

Now if I hit the gas HARD, sometimes the hesitation is not there.

You guys have any suggestions? A full tune up was performed about 5 days ago.. (plugs, wires, cap & rotor, air filter) TB was cleaned too.

Did you use Champion spark plugs?

Yes.. This problem has been for a long long time. Probably for a few years. Just recently it's been getting worse. HP seems to be suffering too. It take more peddle travel than normal to get up to speed and or to get her to downshift.. This is where the hesitation comes into play ( when I give more peddle travel to accelerate)...

O2 sensor have NOT been changed.. The only sensors that I ever changed was the TPS..

How about a possible plugged catalytic convertor?

That's what I was thinking but wasnt sure how to figure it out.. The Cat WOULD make sense for the fact that the feeling you get when hitting the gas at any speeds feels restricted... I also noticed a decent power gain either first thing in the morning or just once in a while..

You can use a vacuum gage on the intake to determine if engine is breathing and exhausting properly.

The most basic way is to remove it and drive it a short amount of time.

Thanks AB.... I'll try using the vacuum gauge in the intake side and get back to you with the results.. Thanks again for your help..