Do you want to be a guinea pig?

How long do you want it to last? Scotty has talked about this in his videos with the takeaway that no way will that twin-turbo setup have the same longevity as the V8, and it won't even get much better mileage if used for towing or carrying loads.

I would keep what you got, the last year of the naturally aspirated V8 Tundra.  The all new generation starting with 2022 model year is more complex and going to a twin turbo setup on the even-more-complex Dynamic Force Series engine platform mated to a 10-speed automatic transmission - I just don’t see it lasting as long as the previous generation(s) Tundras.

Also, it is wise to wait a few years to see what issues (if any) come up on the new Tundras.

I would keep the 2021 model. Those V8s can virtually run forever. Who knows how the new powertrain holds up overtime. 

Hell no.

Keep the V8. Twin turbo V6 is like rolling the dice. Do you feel lucky?

Keep the 5.7. I drive a 2007 Tundra 5.7 with 224,000 miles daily.  My daughter drives my 2000 tundra which is 22 years old with 240k miles. The new one is having lots of turbo waste gate failures.  Wait a year until they fix the issues.  My 5.7 tundra is reliable.  I think the 2000 tundra with the 4.7 is the most reliable truck ever made. If you replace the timing belt and water pump every 90k miles.