Stock is a 195* t-stat.
Considering the age...
Radiator or AC condensor in front pretty nasty/dirty killing air flow?
If Dexcool, just drain all that, garden hose it all out as much as possible and put the green stuff in. Most new green stuff is dexcool compatible. So don't have to worry if you have a little dexcool left in there. Not gonna destroy the whole thing.
Check fans are both spinning.
Hows the heat? Back flush the heater core while in there.
Replace TStat with a new one while in there also. Pick up a 180*.
Check for elbow and intake leaks and replace as needed. If intake manifold
gaskets still the old crappy plastic ones, buy the newer aluminum ones and swap
em out. Not all that bad.
I myself had two issues. Heater core clogged in my 98 GP and a fan was dead.
Back flushed the core nice and clean, and replace fan and all was good. Knew I had something
going on as even in cold weather at idle the temps would start to rise and heater temp output would drop.
Also I havent been an Ultra, is the ECT temp a digital read out? Or going off gauge, as the analog gauges
are always way off.