if you put a ps cooler in, you would prob see improvement. beings that you arent in a tropical environment, im going to go ahead and say you got a weak pump.
FIRST FIRST FIRST is your fluid ok? Clear/Red, no debris, right level? Vent in cap is okay?
First thing first, assuming you still have v belts, check tension(hell even serp) is it slipping on the pulley?
if that is good, pulbelt off, check shaft for play. pump pulley and shaft shouldnt be wobbly or in out/side side machine, should be firmly set.
if that is good, i would flush your PS system and install a cooler, if a square, any universal can work but if a gmt 400, a stock rad-placed ps one would be easiest to fit. it screws into the core support.
if problem persists but all checked, i would check your pressure with a ps pressure tester. if pressure bad, pump replace. if pressure good, you have a fluid flow problem in your gearbox(check for binding or other issues in steering components, like underinflated tires.)
Some have used seafoam trans fluid conditioner/cleaner, you would be removing some PS fluid, substituintg. driving for a day or so, flush whole system etc. if you have gunked up valves.
