1997 Chevrolet Suburban transmission

There isn't much you're going to do yourself with this. The first thing your mechanic will do is connect a scanner to see if there's any diagnostic fault codes related to this problem. Next, it will show if any shift solenoids are being activated by the computer. A pressure test may be needed to see what is happening in reverse. If the reverse servo is getting pressurized but there's still no reverse, suspect a broken band. Replacing that is very involved. On older transmissions that were hydraulically-controlled, the clue was when you drive in "low" or "1", it would still up-shift to second gear. I don't know if that is still a valid test with electronically-controlled transmissions.