I just changed the filters on my 4000MH transmission. Total time is less than an hour as this is really a pretty easy procedure.
Check your filter and fluid change interval here:
There are several references for this procedure, but I used this one:
The first half is a 1000 trans, skip down to the 4000 tutorial.
I purchased the Allison filter kit #29558118 (same as #29548988) here:
Pretty simple really. It is not necessary to drain the fluid before changing filters. Just unbolt six 15mm bolts for each filter. I did one filter a time starting with the Main filter (passenger side) as less fluid drains from it. Place a drain pan under the filter cap before removing it to catch the fluid. I lost less than 4 quarts total. Replace the o-rings and gasket for each filter and place the new filter down onto the cap. There is also an internal o-ring inside each filter that fits down onto the cap. Lube all three o-rings and the gasket with clean ATF. Re install the filter and cap and torque to spec in a cross pattern. Then do the second filter the same way.
My trans dipstick is accessed from inside the coach. It had a yellow plastic tag saying to use Allison Transynd only. I added 1 gallon of liquid gold.
I started the engine and selected D, then R, then N and ran the engine for a few min. I then pressed both the up and down arrows simultaneously to check the fluid level. All is well again.