Part of when a transmission shifts is the actual torque demand. Unless the engine is going way over the torque peak there isn't a problem with holding gears too long. Contrary to what some people think, it's not horsepower that tows a load, it's torque so with a gasser the engine is going to rev into the torque band.
True, I just drop it out of T/H until it shifts back into 8 and then turn it on again and cruise in 8.
Probably right on the bubble between 7 & 8th gears for the speed/load.
T/H seems to like to keep the rpms close to or above 2000 rpms no matter the gear on my truck.
Which is why I generally don't run T/H when empty.
I actually wish my truck would lug the engine a bit more - heck I mean even a bit, it downshifts at the sight of any grade.
It esp. annoys me on the level (like in Florida) going over the overpasses. If it would lug just for a second or two, I would be over the overpass and actually on the downhill side of it.
At 70 mph I am at 1900 rpms in 8th, so while the extra few hundred rpms dropping in to 7th doesn't appear to bother mpg (good or bad) vs. 8th, it is more of just a noise, used to lower rpm deal for me.
My old 5.9 Dakota pulled harder than the 5.7 in the lower rpms.
Decel and braking are fine with a load and using T/H, the slightest brake pressure and it downshifts another couple of brake pushes and it downshifts again.