Truck won't turn left

[Rawze]

Something is obviously causing the fluid to overheat. Alignment can do this if there is no PS unit cooler. A slight pull all the time under heavy axle loads can slowly heat the oil to excess temps. As well, are you running ATF in them? that is what TRW recommended as the best oil to use I went through re-build training on them.

Solving your problem will require you to investigate why the oil is overheating going down the road. That is not normal. Any time you have an internal leak,.. or there is a constant strain/slight pull on the unit, it will simply get hotter and hotter unless there is a cooler installed.

Is it even running in its base detent position going down the road? -- or did someone jack your alignment and you just can't feel it in the steering? -- I have seen some pretty bad alignment that does crap like that and the truck not even pull to one side. To check the base detent position,.. jack the front end up on both sides so that the steering wheel can turn freely and crank up the truck. See where it "wants" to sit (the PS units center-point instead of the steering wheel center -point) and compare that to where it sits going down the road.

If there is no internal leaks causing excess heat, and it is simply a matter of your demand being too much for a non-cooled unit,.. simply install a cooler on them and call it a day.