I've got to update options. One is a Murray rated at 16 psi and the other is Napa is rated at 22 psi. What do u think?? Is that a stupid question?

 

You're XJ sounds just like mine when I had a bad head gasket.... With your engine COLD take your radiator cap off, and start the engine, and watch the coolant. See if it bubbles/surges. if so, you may have a bad head gasket. Check your oil, look for any milky film on the cap/dipstick. If you have bubbles/surging, you have a hole in your head gasket. nothing big enough to cause immediate overheating, but pressure builds up in the coolant bottle after longer higher RPM drives, and then you overheat.

I did exactly what everybody recommends against, and used fiberlock to fix it. I did not flush my system after a confirmed leak, so it plugged my radiator, but I've put 5K miles on it with no issues whatsoever with overheating. so I'm calling it fixed. BUT I confirmed I had a head gasket leak with a pressure test of the cooling system. and I could idle in my driveway for 40 minutes + with no issues. it was only after I tried to actually drive it that it would over heat.

 

flushed it last night and Temps are back to normal but bottle still extends quite a bit. I'm probably going to do an exhaust gas test on the coolant system. To see if I have any gases in the coolant.

 

Ditto to the other guys, replace the radiator and fan clutch, you've done everything else. Went through this with my 95, the new radiator was the solution to my troubles(of course that was after the water pump, thermostat, hoses, fan clutch and rad cap.)