Steering loose I need to tighten up the steering on my Suburban. I was told there is a screw to tighten on the underside of the steering colum. Where is it exactly?

At the end of the steering wheel there is your steering gear box on the top of the gearbox in the middle you will see a screw and a nut you need a wrench to lossen the nut and a screwdriveer to tighten it up. maybe your front end is loose you should have that checked out

The problem is not in the steering gear box.
1. check the shaft that is hooked up between the steering gear box and the steering wheel (the one which goes through the firewall, connecting to the steering wheel the joints at the ends could be worn out and loose, all you can do is replace the shaft.
2. check the front-end for loose components such as:
tie-rods, idler arm, pitman arm, center-link, upper and lower ball joints, and all the bushings at the control arms.any loose or worn parts can cause vibration and looseness and a very unsafe vehicle on the road, after replacing any front suspension components always align the front-end. you dont need to align the front-end if you are just replacing component mentioned in 1.

There is a allen/screw on the steering box that is the play adjustment. Loosen the nut around the screw about 1/2 turn and have someone move the wheel. Take the allen screw in one direction. It should take the play out. I can't remember which way to take it. Then tighten the nut to keep it there. You might want to try it one way about 1/4 turn. If it is worse, then take that 1/4 back plus another 1/4 turn and try again.
I would start with a 1/4 turn clockwise.

Also, check the sway bar bushings and both the front and rear chassis. It could another issue. My 93 2WD has both sway bars. The rear links are hard to find. Fronts are a dime a dozen. Could be shocks too.

I rebuilt my Suburban suspension @ 200K miles. Everything was changed. Drives like new.

Watch for Chinese front brake hardware. There is an issue with the finish demensions. The brake caliper tubes are too large diameter. Calipers stick. Use made in US only brake hardware and cailpers. High speed vibration +60 and above. Bad gas mileage. I now get 16 mpg city. Used to get 11 mpg city. The Suburban will push through it, but eats transmissions.