t-case problem?
 

I have a 71 K5 with a 3 on the tree and a Dana 20 t-case. When I'm in 4lo it will kick out of gear. When I'm on the gas and then let off it will come out or if you hit a bump it'll come out of gear. Sometimes it will grind like it's between gears or something. It just does it in 4lo. When it stays in gear it works fine. Any Ideas?

Do you have a body lift? Maybe the shift lever isn't all the way forward?

body lift
 

It does have a body lift. I will check into it tomorrow. I'll get someone under it while I shift it to see if it's not going in. On level ground just putting around it will stay in 4-lo. But I'll check thanks for the reply.

i think you're on the right track, sounds like your floorboard it stopping the shifter handle from engaging completely.. you don't need anyone under the truck, just pull off the shift boot and then you can see what's going on.

another good point! thanks