On my '94 Ranger 4.0l I had a random temp increase and decrease.
After initial warm up I could be driving along, not uphill or down hill just cruising and gauge would go from it's "normal" spot up above 1/2 almost 3/4.
Then it would drop back to "normal"
I could be slowing down and it would do it, or driving uphill, it would go up and then drop back down even before I got to the top of the hill, totally random.
It turn out to be the heater core, on my year(not sure on '96) the heater core is part of the coolant bypass system, so there is no heat control valve on the heater hoses, coolant is always flowing thru the heater core.
Look at your heater hoses if they run from the firewall to the intake and water pump without a valve then '96 is the same as '94 setup.
Core had gotten clogged up over the years, I still got heat out but I have to say it wasn't super hot, defrost worked so never gave it much thought, lol.
New core was $28, very easy to replace, two hose clamps(on hoses) and 4 screws(under glove box), took 30mins., could do in 15 now, lol.
If your heating up happens only when stopped then fan clutch is most likely issue.
If heating up only happens under load(going uphill) then low coolant or water pump issue.
If it is random...............check the heater core
I know on some years/models they used a bypass valve on the heater hoses, this could show the same symptom if it was failing.
Hope '96 is not like the '98, seen here: http://www.therangerstation.com/Maga...eplacement.htm