Lack of power and brake issues.

So, I have been driving my Tacoma a lot of late because I need to be in the office. It doesn't have any trouble hitting 75-80, but seems to take it's time getting there.

The truck seems sluggish. Though I have been driving my 2000 Tundra on 35's a lot lately too.
The Tacoma is 6700 lbs GVW setup with myself, the RTT/Shell/Awning/gear/my tubby butt.

Truck has 4.56's and 33" tires. It might be time for spark plugs.
Oil gets changed every 10k miles with Mobile 1 Synthetic 20k oil, and I do filter changes (both air and oil filter) every 5k miles.

Not sure if it's engine wear (I should pull a sample to send to blackstone). Or if I am just used to the Tundras torque...

Another issue is that when coming to a full stop, the rear of the truck seems to 'drop' with a little bit of a thump. It feels like the u-bolts are loose (they aren't, I've checked them). I wonder if the weight is causing this or if it's time to have the rear brake shoes serviced.

Can I install the 4Runner/FJCruiser/GX rear disks in the axle or are the flanges different?

Truck is at 210,000 miles.