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Message: [QUOTE="me2, post: 384557, member: 3825"] Here is how I hope towing goes with the Cummins 6.7 and 6R140. First off, at any speed more than about 20 MPH, I hope to have the TC on the 6R140 firmly locked except when the transmission is shifting. One of the things that really bothers me about the 5R110 is that even in Tow Haul mode the TC doesn't seem to lock much until the truck is doing 45-50 MPH in at least direct, if not OD. Even when unloaded, slow acceleration requires 2000 RPM due to lots of TC slip. When towing, slow acceleration requires at least 2600 RPM and anything fast has the tach pegged. This is in sharp comparison to the 5.9CR/ZF6 in my F250 where it seldom gets revved above 2,000 RPM when empty and manages to accelerate pretty well. Even when towing, it would seldom go above 2600 RPM. Of course the 6R140 will be under full manual control if I want it to be. The top 6R140 ratios are 0.67, 0.86 and 1.15. Engine speed at 60 MPH in top OD is 605 x 3.73 x .67 = 1511 RPM. At 65 MPH, its 1640 RPM. I'm hoping my engine will make at least 1000 ftlbs at 1600 RPM. I'm shooting for 1200 ftlbs. 1500 RPM x 800 ftlbs / 5252 = 228 HP. This is nearly as much power as a stock 7.3 makes. 1500 RPM x 1000 ftlbs / 5252 = 285 HP. This is as much power as the 6.4 makes in direct. 1600 RPM x 1000 ftlbs / 5252 =304 HP. This is as much power as the 5.9CR makes in 3rd gear at 2700 RPM. 1600 RPM x 1200 ftlbs / 5252 = 365 HP. This is more power than either the 5.9CR or the 6.4L make. Theoretically, if my 6.7 makes 1200 ftlbs at 1600 RPM, it should be a tow beast even in double OD. Having said all that, I'm not sure that I'll let the engine make that much power/torque in that gear. If it made 800 ftlbs at 1600 RPM, that would be 240 HP, which would be more than enough for cruising on flat highways, which is probably all I want to use that gear for. Having said all that, the Ford 6.7 is said to pull 5ers really well at 60-65 MPH in 2nd OD, even on trucks with the 3.31 axle ratio, though they do have somewhat smaller tires than the 20s on my truck. The rating on the Cummins marine 6.7 said that wide open throttle (1165 ftlbs) was to be used less than 1 hour in 8. I don't want to make a habit of cruising down the highway at 15-1600 RPM with the engine at a really high torque load. And that is OK with me, because... The first shift down is 1st OD. Engine speed in that gear at 60 MPH is 605 x 3.73 x 0.86 = 1940 RPM. At 65 MPH its 2100 RPM. I think this is a beautiful gear ratio for towing. Here I definitely want to be making 1200 ftlbs. The marine 6.7 makes 1165 ftlbs at 2,000 RPM. 1940 x 1200 / 5252 = 443 HP. That is 100 HP more than a 6.4 makes wound out in 3rd gear. 2100 x 1200 / 5252 = 480 HP. That is 100 HP more than the most powerful stock Duramax, more than twice what a stock 7.3 makes. I should be able to climb some very steep and long grades at 60-65 MPH with this sort of power, stress free. The engine is running at a perfect speed in this gear for good fuel economy. Its not lugging and its not over revving. The next gear down in the 6R140 is "direct" with a ratio of 1.15. Engine speed at 60 MPH is 3.73 x 605 x 1.15 = 2600 RPM. At 65 MPH, its 2811 RPM. This will be my power pulling gear and I love the ratio. Its a faster ratio than 3rd in the 5R110 and 3rd in the ZF6. It will be perfect for engine braking down long descents, without fear of over revving. 2600 x 1000 ftlbs / 5252 = 495 HP. 2600 x 1200 ftlbs / 5252 = 594 HP. 2800 x 1000 ftlbs / 5252 =533 HP. 2800 x 1200 ftlbs /5252 = 640 HP. I'll probably only use this gear and this sort of power for passing and climbing steep grades. I love the thought of doing long, steep climbs at 50 MPH (2166 RPM) in this gear to save fuel. 2166 RPM x 1200 ftlbs / 5252 = 495 HP, if I need it. I hope everything works as well as I think it will. I can't wait to get it going. Sorry for all the babble. It passed the time while I wait to find out what is wrong with our dog. [/QUOTE]