Per the Allison authorized repair shop near my work...here is the skinny:
Based on my trans. serial #6510135371, here is what will work for my MD3060:
Allison supports ANY trans fluid that meets or exceeds the TES-295 standard. They of course "like" you to use Transynd as they get $$$ from the sale in a partnership agreement but other brands are acceptable as long as they meet the standard.
Old (Allison WT units up to #661009226
VH 660861003 Automatic transmission fluid Shell Donax TA
(meets GM Dexron III and Allison C4 specifications)
Initial fill: 47 US Qts / Refill: 37 US Qts
Allison 29501202 Main filter 1 (2 quarts for filter change ONLY)
Allison 29509723 Lube filter 1 (8 quarts for filter change ONLY)
New (Allison WT units from #6610092269)
VH 10786691 Automatic transmission fluid Castrol Transynd
(meets Allison specifications for severe duty and exended drain intervals (TES ? 295) and GM Dexron III and Allison C4 specifications)
Initial fill: 47 US Qts
Refill: 37 US Qts
Allison 295387231 Main filter Product Line Gold Series 1 (2 quarts for filter change ONLY)
Allison 295387232 Lube filter Product Line Gold Series 1 (8 quarts for filter change ONLY)
VH 10801799 Tag, ?This transmission uses TranSynd??? 1
The MD3060 "should have a 4" deep pan. The filter kit includes both deep filters and both new and old gaskets/o-rings and costs about $52.
You can go with either fluid but a change of type requires a filter change. The synthetic does not really cool the transmission better. It primarily extends the service interval but is more efficient and produces less debris in the fluid. The service intervals are listed below for standard/extreme use with extreme being HD towing, running up/down big hills, heavy throttle use etc.
Dextron III: 25,000/12,000 miles (fluid AND filters)
TES-295 Synthetic: 75,000 (filters) and 300,000/150,000 (fluid)
As you can see, the switch to synthetic extends both the filter and fluid change intervals with only filter changes required in between the overall mileage numbers.
I have linked an Allison document for VanHool buses/motorhomes but it has some interesting data and guides PLUS a picture of the old/new transmission filter assemblies and pans.
Allison Info
FWIW, it lists slightly different intervals so you need to explore this. I may still go to synthetic if for nothing more than the extended service intervals and cleaner internals but I need to weigh the increased costs versus more frequest services.