When Tripp enters the garage and we see his truck in progress, he states that the truck will have 425 horsepower. The Hemi pulled out of the Terravex truck is not a 6.4L Hemi (only a 5.7L Hemi) and even if it was a 6.4, they only produced 410 horsepower in the heavy duty trucks. The 5.7L Hemi makes 375 horsepower in the trucks and 390 horsepower in the cars.
When Tripp is talking to his truck and he says "you'll have the heart of an elephant", it refers to the nickname hot rodders called the 426 Hemi V8 from 1966-1971, called the "Elephant Motor" for its massive size and weight. It also made 425 horsepower, which Tripp incorrectly states that the engine he pulled out of the truck made.