Guys I have an 89 w350 that we use as a feed truck , the problem has just started , everything will be fine then all of a sudden if is like it slams in park, put it in reverse and it will go about 15ft or so and slam to a stop again then it will go 15 feet or so and the same in forward, I have had this happen a few time now I have tried unlocking hubs that didn't help . I have tried it with the trasfercase in every gear as well if you keep rocking if back and forth it will eventually take off just fine . I was pretty heated the last time it did this to me so I got really rough with trying to get whatever the issue is to go ahead and give up but I cant seem to find the weak link .

 

Sounds like its getting ready to give up the ghost. How many miles on it, and how was it maintained?