The initial filter change on the Allison is at 6,000 miles. It is only the primary filter. When you get the filter it will come with the O rings and gaskets that you need, as well as an instruction sheet. Not much oil comes out. You don't have to drain the pan or anything and the most I lost was maybe a pint that got sucked up into the filter itself.
Later on when you change both filters (I "think" that was around 25,000 miles) you just double everything. My coach came with Transynd right from the factory. Freightliner began this changeover early in 2004 so I would assume that you maybe have Transynd already? I would definitely go with the Transynd if you don't. It will eventually extend your fluid change intervals but you need to change it twice before you reach that level of saturation because there'd still be plenty of dino oil left in the torque converter. It's also a better lubricant and it runs cooler.
Mark & Leann Quasius
2016 Cornerstone 45A
2020 Jeep Gladiator Rubicon
2021 Jeep Wrangler Rubicon