1980 Chevy Truck transmission not working right

Ok I was pulling a friend out of a mud hole when I got him out I was n my way back to the road while I was driving my truck would jerk every now and then almost like I was tapping my brakes and then it was like I slamed the brakes my truck came to a stop I put it in oark to get out and look but nothing when I got back in I put it in drive and I had nothing it would not move but when I put it in reverse I was like nothing was wrong. I then got it towed home when I got it home I tryed it agasin when I put it in drive there was no movment until it hit a high rpm then I would try to move a bit but reverse workes fine if anyone knows what could be wrong or if you have expirinced this please let me know thank you