Truck Forums - GMC Sierra 1996 Truck Won't Go in Reverse

Hello Everybody!
Haven't posted here in a while but hoping to get some good advice to help me out with my son's truck. To update those who don't remember me....I bought this 1996 GMC Sierra Truck last year for my then 17 year old and was having A/C issues but got some really good information from this forum and was able to get done what needed to get it working. All was well with the truck until last night when i got home my now 18 year old is red faced and sweating because he couldn't get his truck into reverse to go to the store to get some butter for his mac and cheese.....He'd called his uncle to check it out and he could not get it into reverse either. They used a chain and his Tundra to pull it out of the driveway so they could drive it around the block and see what gears it got. It shifts from first to third with some fiddling around and they got it up to 30 mph but did not try and go faster than that. It had not been slipping or showing any signs of problems before last night. We live over a hundred miles from any transmission repair shops and will have to have it towed or put it on a trailer to take it anywhere to get it checked out. I am wondering if anyone knows some quick fixes we might be able to use to check it out to see if it needs an overhaul or something else. All comments would be appreciated.....thanks everyone