1978 GMC Classic Sierra 4x4 problems

I've looked all over the forums and havn't found one like this so hopefully someone can help. When i want to buy the truck i test drove it and it was in 2 wheel drive. i couldnt get it out of the snow so i had to put it in 4 wheel, well it has lock-outs and i'v never used those before but i'v heard about them. so i put it in neutral and switched them to lock and pulled the lever on the floor back and it wouldnt work, so i played with it alittle and finally got it to work. Any about 3 days after we bought it we got it insured and everything and took it out. I went about 4 miles and parked at my friends. I was going to see if i could get the 2 wheel drive to work again (we had kept it in 4 the whole time) so i unlocked the wheels and noticed that i had been driving the truck in 4 wheel drive and the lever inside was up or torwards the engine, so i pushed it the only way it could go which was back towards me. I drove the truck around the corner and it felt like it was still in 4 wheel drive then all of a sudden it bogged down so i hit my brakes and the truck wouldnt go anymore. The lever had flipped back up towards the engine and no matter what gear i was in it would just rev up. i tried locking and unlocking the thing and the lever wouldnt go back. I did it in every gear and i tried forever. I finnaly had to have it towed and now the machanic wont get to it till monday. I was just wondering if anyone might know what this could be and about how much it would cost me to get fixed. Thanks

I know its should be sierra classic, oops.

not sure what happened but the older trucks it wasnt a good idea to keep them in 4 wheel if not needed. could be anynumber of things sounds like the transfer bound up if its a chain which it probably is.might have busted gears or just the chain but if it wont go in 2 wheel then it sounds like a gear problem.
good luck

Do you still have this truc, and would you be interested in selling it. [email protected]