Bad Vibrations on Highway and Bucking During Roll to a Stop

Gents,
My truck is a 2008 Pro-4X with 131,000 miles on it and it seems I have been having to do some higher dollar maintenance over the last few years.
At 80,000 miles I bought new front hubs/bearings, bought my 3rd set of Nittos at 88,000, had my front differential rebuilt and the driver's half-shaft
replaced at 126,500, and now I'm having some serious fast vibrations right under my feet, when doing about 35 mph and 65-75 mph.

Today, I raised the truck up on 4 jack stands to run it off the ground....but NO vibrations in 2WD or 4WD when raised up off the ground doing up
to 90 on the speedo..............UNTIL I started to brake. It was like my rear end was not wanting to slow up and was bucking to keep going......
once my wheels had come to a complete stop, I shifted into Neutral, let go of the brake,then low and behold, my rear driveshaft starts spinning
like it is engaged. I slowed one rear wheel to a stop before it started really going fast, but the diff let the other side pick up speed still......

I've noticed for some time(years) that when slowing at a light or to a stop from 35+mph, it always seems like my truck feels like it keeps on pushing or shifting down unevenly when braking to a stop. Like it still wants to go. Anyone else have similar issues?:frown:

QUESTION: could it be that my transmission is needing some work?
- Is it normal for the rear driveshaft to still want to spin when in Neutral without rolling resistance on the ground?