Both are DRW's with the six speed manual.
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Who is Rob? Any way I can get in touch?
Greg covered it. Give him a ring. Then send him something nice. Haha. (We got him a C-130 wooden model a couple of years ago for helping us out to make sure what we were doing and where we were getting parts from during an emergency repair in Nebraska to replace my VP44 on the way to Oshkosh, was sane. He called me back on a weekend -- unheard of in that biz -- and was apologetic because he'd been out of cell range up rescuing another customer with a different problem in the mountains. Super super guy.)
Now you're just down to gear ratios. Heh. I have the 4.10 and honestly, I feel it's too low.
With my Edge Juice w/Attitude and the light tune from the Tow mode, plus a larger single turbo, and upgraded intake with BHAF and 4" exhaust pipe all the way back, I still limit out on EGT when flogging uphill Colorado style at 6% grade with the 12,500 lb trailer on behind, and the Cummins would pull those hills fine by just grabbing another gear, which is what I have to do to get my foot out of it and less fuel flowing to keep the EGT in check.
People have pointed out online that the stock setup will go way above 1350 on grades, towing, and no harm done, but Cummins has a temp limit and a time limit, and the stock truck doesn't have a pyrometer. So people don't notice. I see it, so I won't hold 1350 longer than about 30 seconds to crest a hill. Time limit in the Cummins manual for the ISB is 90 seconds.
(My older Edge won't defuel on its own via EGT or if it does I've forgotten how, so I alarm at 1300F and just get my foot out of it. If I stay in it and accept 1350 the alarm is squalling the whole time as motivation to knock it off. Ha.)
There's just no way to flow more air through my engine. I have the dreaded light "53" block, and any more turbo above 35 psi and I'm going to crack the block and get to see how fast a Cummins will evacuate all of its oil all over the road. So I limit to 35. Guys with the non-53 block are pushing 50 psi through them after studding the head. (We studded my head anyway, since it was off for my head gasket blowout when the turbo was set up wrong and pushed up to 40, towing. Wastegate was wired shut. Argh... didn't see it...)
Pop goes the gasket... and then it still towed the trailer all the way home, 1200 miles, running on five cylinders. Haha. Just needed a LOT of antifreeze! It vibrated a little and was slow to respond to throttle input. LOL.
That MIGHT be a plus of the 5.9. It's not got the emissions stuff that later 6.7s had which also means it's too stupid to quit/give up. Haha.
Only a few things will stop my truck...
VP44... been there done that... and throwing a serpentine belt because my exhaust brake is vacuum pump driven and when the vacuum, pump fails, it takes the belt out. Fix for that is to carry a serpentine belt sized without the vacuum pump and route around it, slap it on, and keep truckin' until you can buy a new pump. (It's a Jacobs, and the PacBrake nowadays might be a better option... air actuated... electric air pump...)
Even losing gears in the NV5600 doesn't stop them... you just have to work around it until you get home. Haha.
Losing the clutch would do you in, also. Easily fixed by upgrading to a performance clutch, which I haven't done yet. Just milking more miles out of my stock one until it says it doesn't want to play anymore.
I still keep roadside on it, because frankly, I'm a wimp, and I'm not changing an inside dually tire by the side of the road... no freaking way. Haha. Tow it somewhere.