mfu & transmission question

[jack van]

So i have 1 mfu 01 and 2 trucks hehe (not the problem). One truck has the all metal 3 speed tranny upgrade from stock and has locking diff in rear the second truck has had locktight on all screws and has the automatic transmission but no locking diffs yet

1ST problem which truck to put mfu in the 3 speed or the auto ?

2nd problem is mfu can ot make up it's mind what it wants to do sometimes
wheels turn when radio used then next day no luck

3rd do i need to used y harness for steering servo and receiver to mfu
:

4th haveing hard time getting differentials to work better on servo