Welcome to TDR. I'd try flushing/changing pwr str fluid. You can suck out what you can with a Turkey baster or the like, top off drive a day repeat, etc. There's a procedure in the FSM on complete drain/change, but from what I've heard getting all the air out of the hydro unit can be difficult. Best/easy way is to pull out what you can and replace with good quality synthetic ps fluid, Red Line is top shelf and I think around $15-20/qt. In your case, since it "may" or "may not" be fluid related see if you can find a less expensive fluid, even just go with "correct" cheaper ps fluid to see if that helps. Bests throwing expensive (and maybe not as good as original) parts at it first, try the simple stuff first, of course if you have a $ tree let me know there's a few little things on mine that I've been wanting to do LOL.
BTW if you go to upper right of screen click on your name, look for signature and create one you won't have to repeat what your truck is and people won't have to ask either.
Hope my $0.02 helps. Keep us posted