Just order a used 145 amp truck alternator. The weak factory LS1 alternator sucks. It doesn't have enough juice to run much off it and they don't cool well and go bad with some regularity. Mine went out while cruising down the interstate. I order a used one LKQ for about $50 and it's worked great.
Check out this thread for what you need and how to do it. The fix for my endless alternator failure's