Drivetrain transmission problem

[heinsite]

I just picked up an 86 M1009 and learning fast that things break often..Anyway, on two separate occasions after turning once left and once right, the truck comes out of gear. When I stop and try putting the shifter in park, it grinds. To correct the problem, I have to place the 4wheel shifter in 4wheel low, drive a few feet, disengage and the transmission is fine again. I also know I probably need Ujoints as well, because when I let off the gas I get the slight clank and the same when I accelerate, I assume these are separate issues, but not sure.
Anyone know why transmission is doing this or where I should start?

 

[phil2968]

Transfer case linkage out of adjustment? Probably nothing wrong with your transmission. Body mounts worn out?

 

[Adrian A]

He has good suggestions to start. I agree completely. Have soldier b put it in drive and hold the brake while giving it a bit of throttle. Do the same in reverse. As you look at the engine it will lift with a broken mount. You also need to check the transnission mount too. If the drive train is moving the linkage will not be happy.