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2003 jeep grand Cherokee with a 4.0 li engine.
I have an issue with the jeep going over 55mph on the highway. will not go any faster. it also seems to bawg down when I try. even if I press on the gas pedal to the floor. I checked out the fuel system with regards to the fuel pump pressures, fuel filter. I even had the catalyst converters check too. everything came out ok. I even changed out the tps. what else could it be? however in the city it drives just fine as wine. don't make no sense! any suggestions and why?

Is your operating temperature up to normal?
When you say bogs down do you mean miss or just won't take fuel?
If you have a fuel pressure regulator with a small vacuum hose on it pull the vacuum hose if fuel is observed replace the regulator.

heat temp is up to normal running around 180-200. I didn't see if there was a hose on the fuel regulator. ill check for that as well. as for bogs down when I'm getting on the highway I cant step on the gas I have to allow it to work its way up gingerly to 55mph. if I try to give more gas to go faster it'll down shift and slow the vehicle down.

I show a 195 Degree thermostat for your vehicle. The ECU doesn't take over until it's up to operating temperature. This unit controls timing and other functions. I would think it needs to be above 190 degrees.

This sure sounds like a restricted exhaust. Was the cat tested with exhaust pressure gauge? Or was the exhaust loosened to allow engine the breath?

A plugged cat will usually seem to have no more power at full throttle than half throttle while accessing to go faster.

Other possible causes. restricted intake air, lack of fuel to the engine, valve timing (worn or jumped chain) , poor secondary Ignition insulation (spray mist windex glass cleaner on the ignition wires and coil in the dark , engine running, look for small sparks to ground)