87/88Firetruck

This is my first time posting to any of the message boards offered on this website, and my identification with third generation hardware is somewhat unorthodox, so I hope I am not too unpure to post here. I have a 1988 GMC C1500 which is primarily stock save for a TPI 350 from a 1987 GTA. I just completed the swap from a 262 V-6 and have only been able to run the engine since yesterday afternoon. The first thing I noticed on cranking was that the alternator belt was emitting the most horrible squeal I have ever heard come from a reciprocating engine. My engine is the type with a single 4-rib serpentine belt for the alternator and three V-belts for the accessories. I replaced the alternator (no huge loss, since the new one is the first I have ever purchased with a lifetime warranty and the bearings on the old one did not quite feel right). The same problem occurred on the next startup. The alternator pulley becomes quite hot in a very short time. I disconnected the alternator cable and ran the engine on the battery alone, and the problem was eliminated. I have little feel for proper alternator load, since I am not physically capable of turning the alternator by hand under load at 1500 or so RPM, but either the belt is slipping under normal load or there is an excessive load on the alternator for some reason. The alternator hot wire runs directly to the junction block on the firewall, and there is a single brown lead on the 4-pin connector which leads to the primary fuse block connector. I suspect that it is for the alternator failure warning light on the dash. As for everything else, though it is probably not relevant in this situation, I have fully integrated the Firebird ECM with the original wiring, and have fully functional sensors, gauges, and ALDL connections.