Sam, Stay with the 3.55's and get a set of the Pro Comp A/T's. They have a 50,000 mile warrantee and offer a great selection of sizes. If you notice any loss in power or economy, remember that Diesels are simple to upgrade. The power available in the Cummins reaches the 1100 FtLb range without stressing the engine. (That was the original number before it was put into a "Light Duty" truck) A few simple mods to the engine and you will see great results. Check out some of the Diesel performance computers to start with...simple installation and good performance boost!