I get that. I went thru automotive school in the late 70's (got tired of working on other peoples junk), then became a construction electrician. I built race cars back in the day, and from age 40-55 road raced motorcycles all over the SE U.S. building and maintaining those as well. I'm very aware of what kills transmissions. The rear end was just serviced about a year ago and the 4wd was serviced at 80K. I just screwed up and never did the transmission on this truck (traded in a 2003 D'max i owned since new at 350K for this truck, and because the Allison transmission was so easy and convenient to service, it got a new filter and fluid every 3rd oil change or approx 30K miles).
Having said all that, yes, I'm a dumbass for not servicing the tranny on this truck. At 62 years old i don't feel like climbing under the damn thing anymore (haven't for many years), so I was going to let my dealer do it when they told me about this issue. Since then have spoken to a couple of others that have said the same thing. Hence why I am asking the question here.