Long Reply
My experience:
Not sure about differences between the Jobs. My 450 is a Job1. I recently pulled a 3 Horse gooseneck w/living quarters that weighs 18k fully loaded (certified scale) on 2 separate trips. The first trip was between Denver and Fort Robinson NE. Drove I25 past Glendo Reservoir, then cut across to NE. on 20. The GCVW was 27160 pounds. It was about 700 miles round trip. At the end of the trip, the trip computer showed the average mileage to be 8.8 mpg. On I25 we were going 60-80 mph. We never got a favorable wind coming or going. On the way to NE. the head winds were 30-35. Between Chugwater and Glendo there were a few hills where 60 was all she could do, but once on the flats 75 was no problem. The second horse trailer trip was between Denver and the Wet Mountains SW of Pueblo CO. That trip was 355 miles round trip, and less one horse so figure I was pulling 16.5k. The drive on I25 was 75-80 mph, or whatever it took to safely blend in with traffic. We went thru Pueblo and headed W thru Colorado City on 160. From there the road is 2 lanes, kinda twisty and starts to climb from 5700 ft to 9400 ft in 20 miles. The speed limit ranges from 35 to 65 on that stretch. I had no problem maintaining the speed limit on that leg on the trip, but the traffic behind me didn’t appreciate when I slowed around the turns to match the speed limit warning signs (If I wasn’t pulling the horses I could’ve gone faster). This is a good time to mention the Tow/Haul feature. When enabled, it allowed me to lightly engage the brake a time or two to cause the transmission to downshift. Although it’s not a true “exhaust brake”, it does help to keep the speed under control without constant brake pressure. I’m sure the vehicles behind me appreciated not seeing my brake lights continuously during descents. Once off the Interstate, the Wet Mountain trip was lower speed and involved steeper grades than the Fort Rob trip. I think the 2011 450, with its lower gear, would outperform any other bone-stock SuperDuty pickup given this kind of terrain while pulling 16.5K. The round trip millage on this trip was 9.3 mpg. One other trip was with my slide-in camper and fishing boat. The 450 weighs 9.1k, the camper 3.8k, and I’m guessing the boat wet, with gear, extra fuel and a 6 pack is 3k. So, that’s almost 16k GCVW. The round trip millage from Denver to Carbon County WY. is ~500 miles. Once again the WY. wind comes into play here. The trip computer indicated 10.1 mpg at the end of the trip. Now a word on the trip computer -- not the fuel economy screen. In my experience, the trip computer has been within 1/10 of a gallon of fuel used when compared to filling-up the tank to the auto shut-off of the pump. So, I figure the trip computer in pretty darn accurate.
My opinion:
My first SuperDuty was a ’99 F350 7.3 which I still own. Unless I win the Lotto, I will never part with that truck. Well, on second thought if I win the lotto I can get a bigger garage to park her in. The 7.3 is a raw power-producing machine that is more like a cross between a Draft Horse and Thoroughbred – powerful and hard running. By comparison the 6.7 is a highly refined, well controlled Warmblood that has been trained in Dressage. I love both of these trucks. Unfortunately the 7.3 is ~7k over its GCVWR when pulling the horses in our living quarter trailer. Don’t get me wrong -- it will pull it, but the liability is too great for me to accept. However, when pulling 16 – 18K I question whether the 7.3 is up to the same level of performance. When pulling with the 7.3 I drive by the EGTs. I feel pretty confident that the 7.3 would have come thru, but would not have been able to pull the load I’ve described under the same conditions, same speed, same comfort and same safety as the 2011 450. I am slightly disappointed in the performance of the 6.7. Even when empty, I can feel what seems like a deliberate reduction in power when mashing the pedal to the floor. In my opinion, this is partly due to the fueling/boost profile that is meant to keep the truck “green”. In other words, the emissions control system purposefully de-fuels the engine to maintain a clean burn regardless of load. Apparently the days of pushing the pedal to the floor and creating a big cloud of black smoke to get to the next stoplight or pull your load up a 8% grade are over.
Summary:
I own a 7.3 and 6.7 SuperDuty. I’ve driven a couple of 6.0’s. I have only read about the 6.4. If you are looking to upgrade to the 6.7, and your towing in lower elevations, or generally flat terrain you might want to consider a new 350 with the 3.73 gears. Several times during our Fort Rob trip I was questioning whether the 3.73 would’ve been a better choice. My gut feel is that the higher ratio is a better choice for interstate pulling. But, if you’re going to be pulling thru steep grades at lower speeds the 4.30 ratio has great acceleration from a dead stop up to 50-60 mph. Anythng over 65 mph and the 450 is past it's peak power curve -- fuel penality.
