91 Jeep Cherokee; Random Stalling, Please Help

I have a 91 Jeep Cherokee Laredo with over 150,000 miles on it. It runs good, but sometimes it will randomly stall, while i'm driving. This hasn't happened lately, since the weather started getting cold. I have noticed a loss of power. It runs good, I just notice that it doesn't have the power it use to have, before it started stalling. Overall, it has stalled like this about 6 times. A couple times, when I started to go after a red light, it went for about a couple of seconds, then stalled. The other times it just stalled while I was driving (when I was going at a steady 50 mph, it just went dead; I coasted to the side of the road). This has only happened when it was hot outside (I don't know if that has anything to do with it).

The mechanic has no idea what's wrong. No check engine lights come on. I had the speed sensor and crank sensor replaced, with no luck. The fuel pump and pressure have been checked, nothing wrong. Fuel injectors checked, nothing wrong. The mechanic said it's probably a bad sensor, but has no idea which one.

You think the O2 sensor or catalytic converter could have something to do with this? Maybe an air intake temp. sensor or MAP sensor? I've taken this to two different mechanics and neither one has a clue as to what it is. Again, no check engine light comes on.

What's goin on??? Any ideas would be greatly appreciated. Thanx.