Gavril (all except Barstow & T-series) Gear Hunting a lot.

I've noticed a long time ago that the automatic D-Series, H-Series, Roamer, and Grand Marshall loves to hunt gears, but it's more prominent on the heavy duty H-Series' because it's heavier and has a harder time keeping its speed stable. But when you do release the gas and it shifts to top gear, you need to floor it for like 3-5 seconds before it shifts up to higher gear.

Or maybe it's an anecdote for GM's transmission behavior? I don't own GM trucks and vans so idk...

this "issue?" has existed forever, but I only had the resources now to record it:

 

That can mostly be blamed on the cruise control app, it is extremely aggressive, which doesn't mix well with automatics. If you hold the speed manually, the transmission won't do that. However, given a hill or a heavy trailer it will gear hunt quite a bit, which after driving a minivan through the blue ridge mountains, I can say is very accurate to real life.