On high performance applications, I use a lot of this company's products. I have had great success with them.
http://www.powermastermotorsports.com/
Any quality GM 10SI should last for you. As LarrBeard points out below, there are some "Crap Shoots" out there. Almost all the low cost rebuilds are coming from Mexico. Those could be questionable. Check the manufacturing location. If you are failing some good ones, 51 CJ3 has a good suggestion. The alignment especially parallel to the front of the block, is almost as important as the tension on the belt for the bearing. The bearing is designed to take load in only one direction.