Exhaust getting louder and other questions...

Back pressure is NOT a good thing, it means a clogged exhaust. A smaller header/exhaust diameter CAN increase torque due to exhaust scavenging but generally at the cost of higher end HP.

 

An optimal back pressure and a clogged - restricted exhaust are not the same thing.

If I were to flatten - smash the end of the tailpipe
that could definately increase back pressure
to the point of being restrictive.

There is an optimal amount of back pressure required
to produce an optimal amount of torque and hp.

While rpm and hp may be helpful on a high speed race cars.
Off road trucks generally do better with increased torque production.
'cause most off road trucks are not WFO race cars.

believe what you wish...
but I think it's wrong to mislead people.

Maybe you should share your opinion
with Toyota and all the other truck mfgr's.
Maybe you can tell them all that they have it all wrong.
And that their engineers are incompetent in their knowledge.

 

So you are arguing for exhaust scavenging. Learn some vocabulary.