I'm just curious, what are you guys who are running 05+ with the 5.9 and the G56 seeing for empty highway mileage, and at what speeds?
If I could stay at 70 or below I could get almost 20 out of mine. Above that and the milage would drop quickly. I changed the tires to 305/70/17 and that did help a little.
If I keep the tach at 2000 or less I can pull 20-21 and I run 33 inch tires... I went 620 miles on one tank driving across the country in June.
I ask because I'm seeing fairly decent mileage on the overhead in with my 48RE - 16 to 17 at 75mph, 19-21 at 65. I was really wanting to get the 6 spd but was really worried that the mileage would suffer due to the higher revs at highway speed compared to the 48RE, so I settled for the 48RE. From the sounds of it, I'm beginning to regret the basis of my decision...
I have an 06 mc 3500 4x4 g56. I have had 285's on the truck for a while and was getting 17-19 mph in town and hwy. I just put on 315's and a cool hose with tagIII and a 2" lift front and back. Went to Texas from Colorado a couple of weekends ago and got 15-16 mph. Last tank in town was 16.5. Previously I was hitting 300-320 miles when the needle hit 1/2 on the guage. Now I am getting 250. Adding 4% for the difference in tire size still doesn't make up the difference. I thought for sure that the added tire height with lower rpm's would make up for the added rotating mass of the larger tire, but it has not. Knowing this now I would have gone with the 285's again.
I have seen 25.2 mpg out of mine but it was only for a little while. Going down hill between Santa Fe and Pojoaque, New Mexico. Then it was all uphill to Los Alamos. When I had gotten home it was down to 24.2. Driving around town I am at 22.4 mpg. On then high way I never go above 65 mph and that keeps the engine at 2000 rpm's. Mileage is around 22.5 to 23.0. Also be advised that my mileage shot up after I hit 20,000 miles on the truck. Not sure why but I could not believe it. I also shift my truck around 1700 to 1800 rpm's. LT.
Mpg My 06 Dually 6spd Got 16-17 At 70-75 Mph Not Towing. I Switched To 3.42 Gears,brought The Rpm Down By 200,now I Get 18-19 At The Same Speed. The Truck Is Stock Except For The Gears.
