Steering heavy / stiff when hot and driving slowly

On my 263k 2006 double cab, I've started noticing the steering would sometimes be selectively heavy and stiff when making a large turn and driving slowly. This seems to be limited to when the truck is hot, and it only seems to happen when traveling under ~15 mph (usually only when making a right angle turn or 3 point turn when parking), and appears to be more pronounced when turning right rather than left (although I've caught the symptom when turning left as well).

I've topped off the power steering fluid at the respective max lines for both hot and cold. Any other ideas of what this may be?

Cheers!

 

Have you changed your rack bushings? makes a huge difference.

 

Thanks for your suggestion. I have not; my thinking is to let my mechanic take care of whatever needs to be done at my next oil change, and simply to gather some ideas for him to look at, as the truck is new to me and him. I will have him check the rack bushings, thanks!