There are two filters in the Alli 1000 series; an internal main suction filter, and the little external spin-on filter. The former is just your routine run-of-the-mill typical rock catcher; it's there to reduce carnage in case of a major event. The later is a unit of moderate efficiency, and it's sole job is the protect the valve body circuits. It filters only 100% of the lube that goes to the valve body. Because it filters 100% flow, it has to flow a reasonable amount, and so it is not a "bypass" filter with really high efficiency, but a typical spin-on that does a good job, but not a great job. For example, the Wix version is beta rated at 2/20=15/25. I doubt that the Allison is much better. However, it's a nice design, and easy to service, and I'd far rather have it in use than not.
I'll also say this ...
Pretty much none of use use our Alli 1000 in our Dmax trucks in a manner than Allison considers "severe" service. I realize that we pull RVs and tractors and Bobcats and the like, and we all want to "think" we're so hardened that we're just really "severe" in our use, but the reality is that we're not. Not by a long shot. The type use we generally put our trucks through, even using them as trucks and not commuters, is "normal" to what Allison defines. To Allison, when they say "severe", they mean what they say:
"Severe Duty Cycle is when the transmission is equipped with transmission retarder or, used in on/off highway vocation, refuse vocation, transit vocation, or intercity coach that stops more than once per mile."
What they mean by severe is when the torque converter is constantly being flashed with heavy torque loads from a stand-still to moving only into 1st or perhaps 2nd gear. Think of an inner city trash truck moving down the block, or a city bus in stop/go traffic, or a heavy footed (low dollar paid) employee who romps the gas pedal in his delivery service down each block. These conditions illicit not only high torque flash to the clutch packs, but also very little air movement due to very low vehicle speeds, and so the cooling loops are challenged as well. But ...
That is pretty much none of us, despite what you all think. When we pull our RVs or construction equipment, we do not have these "severe" conditions present. Allison (and GM at the time) had our use in mind, and therefore our "normal" use of hauling stuff is 100% expected and designed into the Alli 1000 tranny. For example, Wayne (the OP here) uses his Dmax/Alli to haul his lovely RV at 65mph on the interstate, and through the various places like the Rockies. I bet his tranny temp never gets over 225F, if even that. I'm sure his TC locks up past 1st gear, and stays locked 99% of the time, and RARELY is under full torque load (probably 50% loaded at best). I am confident he never flogs the trans in first gear, jerking the RV from a standstill to 15 mph with the TC unlocked, every 45 seconds while sitting in 100F heat, for 10 hours a day.
And because I live near Indy, and work near the Allison plants, and have actually spoken with friends who work there, as well as emailed with a retired Allison engineer who specifically developed the TES-295 fluid specs, I am confident in my assertion that we're not "severe" in our use of our Dmax trucks. And so, if you answer the series of questions correctly, (normal service factor, typical miles, etc) you end up with the spin-on pretty much always at 50k miles FCI. If you answer "severe" in their fluid calculator format, you are inducing a condition that is untrue, and it will tell you to OFCI more often than truly necessary.
If you want to change this filter once, early on like Wayne did, as a precaution, there's nothing wrong with that. But changing the spin-on filter and the fluid more than every 50k miles is a waste of time and money. And there is zero cause to ever change the internal filter; only upon tear down per Allison.