Power steering pump straining?

[DLeach]

Aloha, got a question for everyone. My local dodge dealer is now installing rims and tires on there new 4x4's. Mine came with 285/75's i believe. Problem i am having is that my p/s pump doesnt want to turn them. When i am sitting in my drive way or trying to back a trailer into somewhere tight i have a heck of a time turning my steering wheel without some movement. I had this problem with my old k2500 with 38 swampers, but i could see why then. Am i overloaded the stock pump, the fluid seems to be fine, and its perfect while driving. I dont know, any help would be greatly appreciated,i am a long way from anybody with any practical diesel knowledge. Mahalo.