Most "V" belts require a re-tension after break-in. If you hit the end of the adjustment on your tensioner then you have a routing or length issue. That being said, don't overlook the internal pressures in the A/C, as too high a pressure can cause compressor lock up; possible faulty high pressure switch, or a blockage some where in the freon system. If there was one belt driving all the accessories, to begin with, groove alignment of the belts may be the problem. Is there any sideways deflection of the belt when installed ? If the P/S pump drives off the A/C comp. does the P/S work OK until the belt starts to slip. 2 grooves on the A/C may not be an indicator that the P/S is suppost to be driven from there. Is the P/S pump slide mounted for adjustment ? Is there an empty groove on the crank pully ? I don't know if looking at a 94 GM truck manual for routing would be any help, but it might be a place to start.