high engine temps

i have a 96 with the 4.0 and ax15. i have trouble with engine temps in the summer (in traffic and steep hills only) and when i am 4 wheeling. But the temp is fine just driving around and on the freeway. When it heats up it almost gets to the red and then the fan kicks on and the temp goes down to normal. And if i turn the heater on it never heats up, it stays right at normal operating temp. Any advice would be great.
Thanks
Ben

Try checking your mechanical fan clutch. That is the fan driven by the serpentine belt. There is no scientific test for it, but a quick check is easy.

When the engine is cold and turned off, you should be able to turn the fan by hand easily.

When the engine is hot and turned off, you should be able to turn the fan but it will have much more resistance and it should not spin freely.

Hope this helps, the clutch is not too expensive. I would go to NAPA or a dealer for it.

Another way, engine cold, hood open, start it up, mechanical fan should roar for about 30 seconds then quiet down as the fluid repositions itself inside. Not scientific just anecdotal. Bad ones generally are quiet all the time. Your symptoms are classic fan clutch OR the tension on the serpentine belt is low.
What kind of maintenance have you done. Generally a 95 by now should have had a new rad [depending on milage and maintenance], tstat. It is after all 10 years old. Same with hoses. I just did my 98 because the water pump was leaking a bit so I did pump, rad, tstat, cap, OEM jeep hoses because the OEM hoses have the spring in the lower hose and the external hose protectors as well as the clamps already installed on the heater hoses.