I agree with Turner's comments about the power steering pump. I experienced a similar problem on a previous coach. I would drive for a while and everything was great, then all of a sudden the rig wanted to go off to the right. After i fought the wheel for a few seconds, it returned to normal. Then a bit later, it'd pull to the right again. In this case, the problem turned out to be a combination of events that caused the power steering belt to loosen just enough so that i had no power steering assist. You might think that it would still want to continue straight even under that condition, but it didn't! Finally ended up changing out a smog pump that was on the same fan belt as the power steering pump.
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