engine overheating

Hoping for some community insight on whether to keep dumping money down the black hole. I own a 99 TJ 4--cyl, 5 spd, approximately 170,000 miles. In the past 6 months, I've replaced the battery, distributor, plugs, wires, heater core, serpentine, tensioner and idler pulleys, coolant...

Ok so long story short, the 2000 TJ engine heats up on some strenuous hills. Only noticed it once but it was climbing on some others here in PA on route 80 that i thought it shouldn't have. Have an electric fan that came with the Jeep (not removing so lets stay on topic), and was debating a...