here is a quick tip that helped me out without having to upgrade to a new servo just yet.....
Check the plastic pillow block screws on you front hubs. i made the mistake of tightening them down all the way after complete tear down and clean-up and could not figure out why i had no steering at all. did a little reading and discovered that was my problem. Take the little blue rubber end caps off and loosen each one about a half-turn till you get your steering back to the way you want it. took me about 5 minutes of tinkering and now they turn freely with the truck sitting on the ground at a stand still.