the ten sounds good enough to buy it for that alone. but i agree on the reason neither have much popularity. i want something to pull a large trailer and the 8.1 comes with a good enough automatic to make it desireable for me.
Uhaul uses(d int he case of the 8.1) both of them extensively, nothing but the v10 in the trucks larger than the 10' which is a GM 6.0 now though.
I've only ever seen one 8.1 that died of internal engine problems in my time doing Uhaul road side, seen plenty of v10's pop the spark plugs, but that hasn't happened to me for years, and was mainly on the older ones.
The c6500's they have run into tons of electrical issues, though this may not be the case for the 3/4/1 ton trucks with the same engine/transmission.
The allison is a good sturdy transmission, I am pretty impressed with the 5 speed in my truck, its the first automatic I've had that doesn't act retarded with loads and trying to select a gear.