727 Issues

A few months ago I bought an 89 d100 that had the 440 and 727 out of a 71 Coronet swapped into it. The other day I had pulled off the road for about a minute and when I restarted the truck and started moving again when it should have shifted into second it hit VERY hard and locked the drive line completely. Luckily I was only a mile from home and was able to lock it in first and limp home. I was just wondering if anyone else had experienced something similar or if they knew what caused the problem. I feel I'll probably have to replace it since they can be picked up pretty cheap and quality mechanics are hard to find around here.