RBYCC

The MPH per 1000 RPM is a pure mathematical calculation.
The power output of the engine is not a component of the calculation.
The only thing that you can do to alter the MPH/1000RPM without changing any of the gearing is to change the OD of your driven tires.
More power will accelerate faster but not achieve a higher top speed then lower power with the same final drive ratio.

Power has no impact on the end result.
The accuracy of the speedometer also has a great deal to do with what you try to compare in You Tube vids.
If the speedo is off ( even new the 124 speedos were not that accurate ), then it would appear that different vehicles shift at varying points.

The shift point is also determined by accelerator pedal pressure which translates into transmission pressure on an automatic transmission.
The more pressure the quicker the shift point arrives.
In essence the faster you rev your engine, the quicker the transmission will shift to the next gear.

zach1328

Ok thank you.
I was just getting confused about the MPH per 1000 revs. I assumed the 3.2L would get more MPH per 1k than a 2.8L. I kept seeing the 3.2L's with the same speedo as mine, but ive got the 2.8L which threw me off.

RBYCC

How about an analogy so you can better understand.

Let's assume you have a bicycle which for every full turn of the pedal the rear wheel makes a complete revolution.
The gear ratio woud be 1:1.

Say that a weak ( 2.8L ) person can turn it once in ten seconds and a strong person ( 3.2L )in five seconds.
The strong person can move the distance of one full tire revolution in half the time of the weak person.

The end result is still that both, regardless of time ( rate of acceleration ), have moved the same exact distance