Jeep coolant temperature help

[tsubaki]

I'd really appreciate some input on a 1996 Cherokee Classic 4WD with automatic transmission, AC and 4.0HO engine.
About mid summer I kept noticing the temperature gauge seemed to be reading a little higher than the normal 210 degrees while driving around town for brief 15 minute trips. But after about 30 minutes of intown or interstate driving the temperature would climb to about 230 degrees. Running with the AC on or off seemed to make no difference.

While sitting in the yard with the engine at 2000rpms, I can make the electric fan come on at about 235 degrees. As it also does when the AC is on.
I'm still having this problem with daytime high temperatures of 80 degrees and less. And there is no evidence of coolant contamination.

Here's a list of things replaced so far.
180 degree thermostat
Radiator
Catalytic converter, muffler and tail pipe
Fan clutch
Water pump
Temperature sending unit

Any ideas???