I have a '93 K1500 Z71 with an automatic transmission that decided to stop shifting with no warning. I drove the truck into work, and on the way home it decided to not shift into the overdrive gear. I can manually shift the transmission from first gear to second, but it will not go from second into drive. Anyone have any suggestions?

On level ground, when hot after driving for a while, in park, is it at the full line on trans dip stick?
Have you ever serviced the transmission with new fluid & filter?
A OBD1 scanner may provide more insight with stored problem codes?

When the problem first occurred there was no fluid on the dipstick. I put 3 qrts in, went through the gears, and checked the level in neutral on level ground. The level is good, and the problem was still there. I even tried manually shifting through the gears. First to second is good, but going into drive or over drive is where the problem is.
I am not sure if the transmission has been serviced, but the parts are ordered and the job will get done.

Sounds like you burned up the 4th clutch.

3 Quarts low, this can overheat clutch packs or worse, unfortunately.
Dexron VI (6) is the latest GM fluid and recommended. When you say parts ordered, do you mean gasket, filter & fluid?
Take a photo of inside the pan, You may see fine black particles,or metal shavings etc.

Yes, the parts is a filter kit. I want to go this route first so I can pull the pan to see what it looks like inside. If I do see black particles, shavings, etc. then I know it is some thing more serious.