My power steering has all but quit working. It works ok when cold but after driving 10-15 minutes it gets real tough to turn. I did the flush/fill with synthetic fluid a couple months ago and it seemed better at first but now it's back to being really stiff. I thought I read a post awhile back that mentioned a heavy duty pump....should I look for one or just replace with a stocker? Any tips on changing one out would be great.