 
Yea I have been dabbing with the schaltmoment values and its script for an while now and they do not do exactly what I've wanted, however, if the value on schaltmoment were to be risen, it would be the actual coupling of the gear take place way more faster, however, the downshift would be extremely harsh as well. 

When I adjusted the engine_j down to let's say 1 about a year or so ago, I have noticed that the up shifts as well as the downshifts were way more smoother. 

Anyways back to inertia, I thought that the transmission component torque gets added onto the engine_j. What I basicly did was used that equation in the PDF file to just manipulate the engine_j values according to that gear ratio. The transmission gets a fixed inertia ratio of around 1.7 or so around that listed. The formula which I came up with was (engine_j/current gear ratio ^ 2) + transmission_j. Now whether or not it is correct or not, I do not know, but I have noticed that the downshifts in the lower gears were indeed way more smoother though.

Oddly enough, I've noticed that the bus brakes way better as well!! 

Well changing the retarder script around for that of the primary retarder actually did solve much of the harsher downshifts.