I'm kind of stumped. I've seen pumps cause that type of problem because, though they still work, they lose pressure intermittently. The drop in pressure causes the wheel to feel like it's sticking or suddenly harder to turn. If you have a problem with the gear box, it might feel more like a mechanical resistance, where the pressure loss feels more like surge, of sorts. The thing that gets me is that pumps usually make sounds that correspond with the pressure drops and harder steering. Have you considered changing the fluid in the system. You can get a gallon of PS fluid at Autozone or O'Reilly's for $14. That's enough to do a complete flush and fill several times over. I know because I've drained and refilled my system at least 3 times and still have a good bit left in the jug. It's a cheap test - much cheaper than buying a pump or gear box. Another random thought... Have you checked the steering linkage assembly to see if any of the joints look bad? That can be another source of mechanical resistance if one or more of the parts are worn.

Food for thought... <img src="/forums/images/graemlins/patriot.gif" alt="" />