How do you put the caliper back in place after installing new pads on a 1999 Chevy Tahoe?

If you're dealing with a lack of clearance to either side of the rotor after you've inserted the new pads, you need to first compress the caliper piston using a large C-clamp and THEN insert the new pads. Doing this will provide the necessary clearance.

If you've already compressed the piston and inserted the new pads and it just "doesn't seem to fit", the piston is compressed too far and the top edge of the inside pad is interfering with the alignment of the caliper to the mount points. Try jiggling the pad towards the center of the caliper to remove this interference and line the caliper up with the mount points.