Valvoline Premium Blue is Cummins' formula brewed by Valvoline. It's what's in the motor from the factory. No need to change it until it's first 7500mile change interval but change away if you like. I never change the oil early. There is no break in oil anymore and the motors are assembled now with such precision and ready to go tolerances, even my new Hemi says 50miles below 50mph and then give it an occasional full throttle (that was fun )operation.
We towed our 10,040 lb 5th wheel just like we've done with our previous Cummins powered Rams after 500 miles. I started out thinking I was going to tow around 50mph and then the darn thing tows so easy I wind up running 60mph for a while and then look down and it's up to 65mph. It creeps up to 70mph very easily but I'll back it back down to 65 just to be closer to 50mph.
We now have just over 900 miles on it. It has the same 10.5" rear end that my lemon '03 vibrating moaning whining driveline Cummins Ram had in it. But this one didn't burn the paint off the differential cover after a good interstate tow. We had a 15mph headwind too so it had the opportunity to get hot like the last one did if it was going to.
Aside from the rear end running hot and the driveline vibrating to beat all, I think my standard output Cummins was putting out less than a standard output Cummins should. Although at a higher rpm, 2600rpm at 65 and 4200rpm up the Sunshine Skyway Bridge in second, the Hemi maintained whatever speed I wanted to drive. So I'm now thinking DC might be managing the torque of the Cummins in O/D a little more than they're letting on to. Just my ever so humble opinion based on my observations of each that I've owned and towed the same 5th wheel over the same terrain with in the same trucks with Hemi and S/O Cummins.
My '95 auto was a poor ol' mutt with 160hp and 400ft/lbs. My '98 5spd/4.10 with 440ft/lbs and 235hp was unstoppable but noisy at 2500rpm/70mph. My '01.5 auto/3.54 S/O 250hp/460ft/lbs was kinda sluggish too. Then the '03 nightmare...
Just for what it's worth, the Hemi gets 15.5 around town very easy suburban type driving. 17mpg highway 70mph and 8.7 towing the high profile 5th against a strong headwind Sunday heading north up I-75 in Florida and 9.2mpg with a strong cross wind. No chance to drive on a calm day yet with the 5th. The Cummins in the same situations got 16-19city, 19 at 70mph and anywhere from 9.6 to 12.5 towing depending on wind and speed. I tow 65-68mph normally.

 

I find your hemi fuel economy reports really interesting. My hemi '03 1500 quad 3.91 & tow package got a whoppin' 9 mpg towing a bike trailer at 70. Only 11 mpg at a steady 60 on the flats. Granted, it's a 1100 pound trailer & it did have two Harleys on it, but it's an OPEN trailer!! Not pushin' much wind at all. My hemi must have been the dog of all of 'em. Heck, it wouldn't spin a tire. I see lots of threads where hemi owners brag about doing smoky burnouts. Not mine. 14.5 mpg running 70 empty was best. During the nine months I owned it, twice it just stopped running for a second or two. Warning lights flashed, chimes dinged, then it would start up again. Dealer "could not duplicate condition". Just a dog. Traded it in on my '04 CTD.

 

Musta been something wrong with your Hemi as there was something wrong with my '03 Dodge. I don't know about smoking the tires. I haven't tried but it is very peppy. It'll downshift to 1st at 35mph and flat sit you back in your seat. Then when it hits second, it flat sits you back in your seat again. By that time I'm doing over 60 and have to back out of it. As I've said in my previous posts before I traded the Cummins for the Hemi, I'll never buy another vehicle without a good interstate test drive first. I got burned with my '03. One of my co-workers has a 4X4 2500 Hemi auto/4.10 and he's getting 11mpg in town and on the road. Another co-worker with a 4X2 2500 auto/3.73 like mine is getting mileage the same as mine. His is also a lively one. Dodge doesn't seem to be very consistant. But at least they're consistantly inconsistant.

 

Yup. I had the same numbers as you (on good days) on my '03 2500 Hemi. It would spin a tire (that's one) if I got on it, and my wife beat a vette off the line with it and that really got him PO'd. I drive a good 30K a year, and got tired of having to fill up. I love the CTD, and really love the mileage difference.

 

I wound up downtown today in the thick of snowbird traffic. My o/h average went from 14.6 to 12.2. For that to happen, mileage must be around 10 in downtown city traffic. So you're probably right. But most of my driving is out where I'm getting 15~mpg. I'm still happy with it. My payments are $94 a month lower to offset it and it has 0 vibration.

 

The number one concern that you will have is the proper breakin of the ring and pinions. Don't let anyone fool you into believing its not important by saying "I hooked up a 10 k fiver and let 'er rip" If your new truck has very few miles on it ,like 4 or 5(as do most),then follow the directions of the proffesional drivetrain builders breakin instructions. Just do a search and you will find them. I won't go into specifics , but it is as simple as driving with a light footfor about ten miles ,stop until the diff cools down. Repeat again and don't tow for 500 miles.Wearing the coating off of a new set of gears to fast will overheat thing real fast. Some diffs just peak at a certain temp and drop down to an acceptable level when not given a cool down period and other gaw and score then become nice and noisy until there premature failure !!!!!!!!!!!!!!!!!!!!!! (flames on , I,m ready)