I have an 86 gmc suburban 4x4 with the rotten 700r4 trans what I want to do is swap in a th400 out of a military cucv what I'm not sure of is if there are any secret tricks to making this swap,and I know the military version has no passing gear and is a 3 speed but it is much stronger than the r4 and cheeper to build up.  

there's really no tricks-it'll swap right out

good luck