I recently picked up a 1992 Jeep Cherokee Briarwood, and its a kick-*** truck with quite a few issues, mostly cosmetic though. I generally drive short distances, ut when i take it out on the highway the coolant tempature gauge slowly climbs until it goes into the red. It has coolant, and lasting the heat doesnt ake a difference. I also tried seeing if it would overheat whle just runing, which it doesnt, what else can i test or what could it be?
Anything is appreciated

 

I'd start by flushing the cooling system and replacing the thermostat. If the cooling system is gunked up, that may be enough to fix the problem.
The next possibilities would be a radiator with restricted flow, or a water pump that's got a worn impeller.
Nothing in front of your radiator that's restricting the airflow is there? Cooling fins clean?

 

Overheating only at highway speeds normally points to a faulty water pump.

 

Agreed, the impellers deteriorate over time and don't move enough water through the system. Could also be a slipping belt, a lower hose that has deteriorated & is now collapsing or the radiator doesn't flow enough water. I would check for them in that order.
Report back on what you found.