False. 2wd to 4hi and 4hi to 2wd is a shift on the fly up to 55 mph in gear. Manual recommends letting up on the gas before doing so. That's how the manual says to do it, and I do it all the time with no issue.Also when going from 4wd-2wd the trans needs to be in neutral same for going from 4hi/2wd to 4 low.
Manual requires you to be in Neutral and rolling at 2-3 mph to shift from 4hi to 4lo and vice versa. That said, I have not been able to do this successfully, I always have to shut the truck off, shift into 4lo, and restart.