Has there been any comparision testing on the two? Like when Truck Trend magazine hooks up a 10k trailer up to the big 3, and see's who can pull up a hillthe fastest. But I would like to see a testwith just the 5.9 vs 6.7.The 6.7 makes more HP and TQ, and the 6 speedauto should be able to keep it in the power band better. Soit makes sence that it wouldpull a 10k load better. But does it?

 

I havent seen a comparison personally but if given a choice, I'd stick with the 5.9. no emmissions (except the cat) so there is less to deal with long term.

 

All things equal stock versus stock the 6.7 should easily win it has more power not to mention thebetter gearing.

 

The only comparison I can tell you is between my truck (5.9) and two friends that have the 6.7's. No contest.....6.7 hands down for power and roll on speed. And my truck ain't stock. However mine gets much better mileage. I avg. right at 20 and the best, repeat best either of them has evergot is 14, their average is about 12. Neither of their trucksis truly broke in yet so time will tell there. But I'm willin to bet the only way they'll ever see 20 is downhill until someone comes up with some mods for them. The dealer I bought my truck from and is also a personal friend, had a 6.7 demo and I asked him how he was doing for mileage with his, told me the best avg. he ever had was 15. Highest for one way trip was 16,that was 125 miletrip to Portland but mostly 13,14. Nice truck though..some guys on this forum seem to do better