My son has an 89 S10 Blazer 2WD, 4.3 Liter with Automatic (I believe 700R4). While driving it recently, the driveshaft fell out while driving down the road. Not sure why it came out, U-joints looked good, bolt for one of the straps was broken. After putting another driveshaft in, the transmission kept jumping in and out of gear, like it was out of fluid. Drove about 3 miles and transmission quit all together. I checked fluid and it is full. Does this sound like time for another transmission, or is there a possibility that something broke when driveshaft came out.

Thanks for any input you can give me.

When your driveshaft came out you must've leaked fluid all over. If you didn't, then something was wrong. If it doesn't work at all, trying flushing it and perhaps goof around with the shift servos/valve body.