Head gaskets really not an issue on these...lower intake manifold gaskets are.
My '97 has been through a shitstorm of cooling system problems in the last year. Started with the thermostat not being able to close and no heat last winter. Replaced that, then the radiator developed a leak, the tank on the side receiving water from the motor got brittle and cracked. Then it blew a small throttle body bypass coolant hose. Then the lower intake started seeping, then gushing coolant one day. Took the motor apart for that pain in the ass, then it blew a heater hose, so I did what I shoulda done before and replaced all the hoses. Now I've got a slight leak back by the firewall, suspect the heater core. Oddly enough the water pump I replaced at 70,000 miles and have added another 110,000+ since, and still not leaking. But easy as it is, I'll probably put another one on soon...it's gotta go sometime.
I don't know how uniform the temp gauges are on these...probably not very...but mine has always run rock solid at 1/3, and will go up over half if idling on a hot day without the A/C on (no constant radiator fan operation)...fans kick on just before 2/3, and it settles quickly back to 1/3. Takes a long time to build high enough to start the fans again.
My first impression on hearing your story is you've got trapped air and it's preventing the fans from cycling properly, this is common on this motor. That would be where I'd start...and if air was found, next I'd wanna know why it was there....