Running heat helps.
In past two years have replaced thermostat and water pump. Now running hot. on 1996 Dodge Ram Van 2500
poss blockage in cooling system suspect radiator
1 more answer , 2 more comments
Due the age and history I suspect the radiator may not be doing the job as it should. Also if it has a fan clutch that should be tested also.
Also had radiator rotted in November.
I still would ot rule out that the radiator could be cause of problem. You may need to have a technician check your car for a diagnosis. It may be money spent wisely rather than swapping parts on a guess.