Grand Cherokee 1996 6 cylinder stalls in hills after been driven over a half hour.

What I have noticed is initially when started up and been driven it exhibits no problems, however after been caught in traffic, and possibly labouring for maybe a half hour or so, this vehicle has a problem that occurs intermittently, it appears to be power depleted. Particularly if I have to climb hills, as is required for me to get home, daily I am required to travel for about 10 to 15 minutes climbimg hills. Typically for this trip I would have to stop 2 to 3 times and allow the vehicle to sit with the engine off for 3 to 5 minutes and then commence my trip until I eventually make it up. Anything you can suggest that I may have checked would be greatly appreciated. Little history on my remedial attempts is as follows: I have changed out a few things I thought could have caused the problem. like Fuel Pump, fuel filters 2 to 3 times Plugs, plug wires, Pick-up coil, Ignition coil, speed sensor, oxygen sensors both up and down stream 3 times, just to name a few within the last year.

My first thought is the catalytic converter. I had the same sort of problem with my 1991 XJ & my 1993 ZJ. Both times, the engine seemed down on power, kinda struggled long, and my milage took a nose-dive. I also noticed that the XJ heated up pretty good, but not so much with the ZJ. (ZJ had a 5.2, and the XJ had a 4.0)

One way to do a quick (though by no means comprehensive) check is to get under the Jeep when she's stone cold, and shake the exhaust. Listen right by the cat, if you hear a rattle, she's toast.

The reason it gets worse and then better is because as the cat heats up, the clogged/melted/busted internals will get bigger, and block off flow; when it cools down, the internals shrink and allows more flow. (At least, this is my limited perception of the problem. I don't have the foggiest clue as to how the darn things really work, and I sure don't have a solid grasp on thermodynamics and the laws of expansion. As far as I can tell, it all runs on magic smoke.)

HTH!