My truck will not stay in four wheel drive unless I hold back on the transfer case shifter. Is there a linkage adjustment that can be made? Any tips at all are appreciated...

i have seen broken motor mounts cause that problem, the motor and trans twist and cause the linkage to "pop" the TC out of 4x4.

If the plastic bushings on the shift forks wear out the case will do same thing, worst case being not engaging at all.

Being manual case you can adjust the shift linkage... put case in N with shifter then pop off linkage rod and make sure by hand that it truly is in N, the tit that pops into the case rod has threads so it can be adjusted