Identical l67 engines, very different power levels. Why?

[Gasnmyveins]

I've been driving a lot of l67 cars lately, trying to replace my Durango that somebody totaled for me. Does anybody know why some of these engines pull like a freight train, and others seem just plain weak? I have my suspicions, but don't want to mention them until the jury is in. I'm hoping it's as simple as I think it is. The engines have all been stock, and running smoothly. No apparent issues with them.
Thanks, Gas.

 

[melsg5]

How can someone answer a question like that without knowing the mileage on the cars, the maintenance level, one car has a dirty air filter the other has a brand new one, the octane of gas the owner is using, etc.