desperate for help!

[chevyforever]

ok, this is on my 82 chevy, but i figure that there may be someone out there that can help me out. the truck has a brand new 900 amp Optima battery, a new 63 amp alternator (second one actually), and a brand new crankshaft and water pump pulley.
NOW for the problem. since i have bought the truck, it has gone through 5 alternator belts! all belts have gone at night with all accesories on (lights, radio, heater, and sometimes with the wipers on also). what happens, is what seams to be an intermintent problem. yesterday, I drove to my brothers house which is 20 miles from mine, all accesories on and everything ok. go to leave so i let it idle for about ten minutes to warm things up good. kick on the headlights and the first few times i slowed down for a stoplight, lights go dim and volt meter drops to 12 volts. get going again and volt meter takes a few blocks till it jumps up to 14 volts again, then i gotta stop and drop off some video returns.get going again and volt meter drops AGAIN, except this time it takes about a mile for it to get back to normal along with some squealing and burnt belt smell. so, ten miles later i stop at a buddies house to visit for just a minute. went to leave, starts ok, and is all good till i kick on the headlights, then the sqealing begins. and doesnt stop, more belt burning, volt gauge still at 12 volts. get about two miles and no more squealing because of no more belt. well it was colder than he!!, so i kept cruisin home (8 more miles) at night with all accesories on cuz it was freakin cold. got home safe and sound, the optima saved my a$$. started it today and put it in the shop to hopefully finally figure this thing out before i drive it anywhere again. this is really long but all help is appreciated because i have done everything i can possibly think of and checked about a million things. thanks
chevyforever