I changed my '90 to open, used a GDI 3 core, a 92, and added the 92 heater valve.
Pros and cons - it runs cooler, when it does. When it doesn't, it overheated until I added water wetter. It was very erratic about overheating, I could never pinpoint it until recently when I went through a dozen threads on the subject. I'm working on it.
I would say that your still fighting an air bubble or a bad t-stat. The rad cap is lower than the heater hoses, so I'd park it uphill to help it purge and recover coolant on cool down. Stats need the hole at 12 o'clock to purge, another at 6 helps even more. The recovery tank must be half full and that line purged to the rad neck, which should be filled to the max. The correct cap must be installed - don't trust yourself or the parts house, with this kind of thing OEM has a higher percentage of being right.
With all that, older Jeeps develop corrosion in the radiators that restrict flow which is the primary cause, and corrosion in the block, which is probably the one that gets us. Flushing with "high pressure" does nothing, it's chemical corrosion eaters that remove the problem (unless you were using an 1100 psi spray in the cylinder jackets and blew the hoses off the water pump.)
Beyond that, small head gasket leaks will do exactly the same - overheat - until the gasket finally makes the big exit. Check cylinder pressures and find the one or pair that are 20-40 psi lower, you might have that problem . . .