First, get someone to help you and turn the steering wheel back and forth for you. you should be able to see where the play is coming from. some common problems---
the coupler connecting the steering box and the steering shaft is very common to have alot of play. check all of your tie rod ends. the bearing on the bottom of the steering column can also be worn out. also, like fatboy said, there will be a set screw with a jam nut on top of the steering box(accessable through the hole in the crossmember) that will adjust the play in the gear. be sure to do small adjustments and take your time if you adjust the screw. You can mess it up.