OK !!!!!! Your have troubles with the beveled ring and pinion
#1 You must shim the pinion into the case without the diff in, do this by adding one shim at a time until the pinion is free but has no slop (in/out).
#2 Take the pinion (still on the shaft) out and now put in and shim the diff so it has a very small amount of freedom (will say it took 5 shims)
#3 Put the pinion in and move the shims on the pinion shaft so the pinion has full contact with the ring gear (in/out) I do this with no shims on the diff so I can see and feel it.
#4 Put the shims back on the diff, If it took (say 5 shims) on the diff you'll have 3 on one side and 2 on the other.
#5 Now start moving one of the 5 diff shims on the diff from side to side (say 4&1 or 3&2) until there is a very small amount of freedom between the two gears.
#6 If the gears are to tight you will feel the gears when you turn the diff in your hand, move the diff shims until it's free but has very little slop.
Man that was long
....I hope you understand and this helps.
I see you have been having this problem for some time now.
I had to do this on my mod HPI pro4, also shaft drive.