The mysteries of Horsepower and other things explained

So why don't trucking companies use a couple light weight Eco motors:

remove 1 big heavy expensive oil change diesel that makes 450hp & 1650lb-ft of torque that doesn't matter...

replace with 2 x 365HP Eco's that would make 730hp, but still deliver 420lbs-ft of torque down the drive line... but that doesn't matter - so this arrangement will "smoke" the big lazy 15 litre ISX ...

right?

Think of the payload increase getting that 3000lbs diesel out of there...