You should get on Ruttingrhino.com and check out the Jbs Hot Rod sheave. Its the only way to go. IMO, stay away from anything with a shim kit. The hot rod sheave will give you the most low end power and pull hard all the way up. It will definately turn those 28s well! I have the hot rod sheave and wow! It is the best mod you can do and give you the best benefit. You can go over to rhino forums.net and read the reviews. If you choose, you can send your sheave to james (wv hot rod rhino) and he will mill it for you for a lower price. You cant go wrong and youll love it!
Let me know if you have any questions, and tell Craig at rutting rhino.com or James at Jbs that hymarker sent you!