AutoZone has our power steering pumps with reservoir for about $70 + core. If you do it yourself you will also need to rent a power steering puller kit from AZ as well. Fairly easy job and the biggest rookie shade tree can do it in just a couple of hours.
The "pulling" while driving is probably unrelated to the PS pump problem. Like NC said, stuck caliper pin in the brakes. Could be any number of steering related items under your truck.
Crawl under your truck, have a helper (with engine running) slowly work the steering wheel back and forth about 50 times. As they are moving the wheel left to right watch for any slack in the steering linkage. Better yet, carefully put your fingers on the actual joints so you can feel the separation. Next, jack a front tire off the ground. Grasp the tire putting one hand and 12 Oclock and the other at 6. Now try and wiggle the wheel. Do the same at 9 and 3 O'clock. If you feel movement (more than just a teeny tiny bit) its time for ball joints, wheel bearing and or maybe tie-rods.