That is why they bother putting stripes on roads with more than one lane.
OP I do drive a Z71 4x4 but its in 2wd 90% of the time and never needed it at the ramp yet. It's always better to have it and not need it than to not have it and need it imho. And yes I always set the E brake before I get out of the truck on any ramp. YouTube has way too many trucks that ended up in the lake I don't want mine there.
This is how I load /unload my 18ft on my own.
Once arriving at the lake before ever getting on a ramp I do everything that can possibly be done. My phone, wallet, hat, tackle, cooler, etc is all onboard before hand. Both buckles are removed, the transom saver is taken off, unlock all lockers (easier to me done here than later), instal the drain plug. Then to the front of the boat. I remove the winch strap and attach a long rope to the boat. I tie off the excess in the bed of the truck in a manner it can peel off more rope if necessary as the boat drifts free of the trailer. I then unplug my trailer lights. I had a incident once where I blew the trailer light fuse while at the lake. Since unplugging them before entering the water I have never had it happen again.
Our lake is usually not a issue with other boaters but once I commit to the ramp I try to run my plan smooth and efficiently. My boat comes free from the trailer just about the time my trailer fenders go under. My boat comes off pretty easy as I have pushed it off many times as it didn't quite drift free. Once it clears the guides on the back of the trailer I untie from the truck and just pull the boat over to the side of the ramp. Gently try and get it lightly stuck where it will sit long enough I can park the truck roughly 2 minutes away as our parking is right beside the ramp. Our ramp I use doesn't have anything to tie off to so I just be very careful and leave plenty of rope so that if it somewhat drifts I can still grab the rope when I get back from parking.
Pretty much do everything in reverse to load it as I did to unload it. If it's calm I have shoved the boat out far enough I pulled it over and back into the guides of the trailer and pulled it on far enough I hooked the winch strap and finished loading it, But I have also drove it back on. I think it was almost as fast just pulling it on the trailer with the rope. But if there is any wind it ain't happening.