How is the 4.0 V6 in the Longevity Department

I think you're right.

Personally, I'm not concerned about running high RPM's. Think about a Corolla, or other 4 cylinder cars. They'll be at 3K+ RPM's constantly on the highway, and generally the motors outlast the bodies.

 

My first truck was a 4 cyl Tacoma and I think you would have to put in a lot of effort to ruin it prior to 300k and I suspect the engine itself will outlast the rest of the truck.

 

I wonder if those were based on the 22R block. Those were notoriously unbreakable. I had one in an '85 Celica. Not fast, but decent torque.

 

Google tells me the first gen 4 cyl was probably the 2RZ-FE (3RZ-FE in certain 4x4, but mine was 4x2)

 

Yeah. I was wondering if if the "RZ" motors were related to the "R" motors. I thought I read that the "GR" motors were somehow based off of the "VZ" motors. I could be wrong about that, though.

 

Gearing / transmission has a role as well. I have a 2018 Platinum Tundra and a 2020 Pro 4R. Both are spinning 2k rpm @ 70mph.

 

Correct. But, generally manufacturers will gear things differently to compensate for the different power band. I'm surprised that a Tundra with torque monster 5.7 would be geared the same as a 4runner.