I am plan to towing enclosed trailer 7x12 with two Harley road king classic and some of stuffs. It maybe about 5k lbs +\-. I am not understand that sixth gear are not for towing purpose? Also I has seen websites that sell fast cooler kit or other brands that make more quarts in nv5600? Should I get it or stay as stock since I only towing a 5k trailer with 2 harley. I did use towing something else but not as heavy like two Harley. I had fifth wheel setup (it was on before i bought it) but I don't own a fifth wheel trailer. I am plan to add one more quart in my nv5600 but before I do, I would like to see what is opinions about it? My dodge cummins was former heavy towing truck that I had found history of previous owners. But my Nv5600 work fine and shifting as normal. I just want make sure it is good to go for two vacations trips. I just want be prepare to do before go for trips. Also I did research on google about overfilling the nv5600, half people said that is not good idea, other half people said yes as overfilling to keep it lube.. Problem is I don't see the proof or live facts that it do or don't help??? It is just talking and opinions...

Depending on the road's you'll be driving on if it's flat interstate your ok at only 5kpds to use 6th. But getting into a lot of hill's you'll be dropping to fifth alot which will eat more fuel but save your tranny. Just don't try to going 70 in 6th the whole time. Last long haul i made in mine (Truck in sig) was a 1,000 mile round trip with a 10k trailer on flat interstate 90% of the way Note(only did 55-60mph the whole way no hurry) and it did ok but by the half way mark my Clutch was warm and driving through bumper to bumper traffic it stuck in 3 and took an hour to cool down before i could drive it. Just keep in mind how the truck feel's and don't push it if it feels odd pull over check it out and if needed give her a few min's. Just to be safe. For the overfilling part it's not a big deal to do and it dosen't hurt in any way it's a splash setup, but i would recommend using a quart of ATF fluid and a quart of Lucas oil Stabilzer. What i done and has helped alot still need a 6th gear sync and a Master Clyinder but can tell it's alot quieter and smoother now.

I am not going to hurry or driving too fast with trailer since I am plan to leave few hours earlier so I can driving at 60 mph with trailer. I has use to get in fifth gear when go up the hill but Indiana and Illinois are pretty flat and not much of hills. Maybe in Wisconsin which I will drop to fifth gear if need to. I am think about just add one quart as not want to push two in and something happen???also I do towing a often around here local but all are flat..

I pull my 5th wheel in 6th gear as long as I can pull it at half throttle. Once I start loosing speed I will downshift. My last trip was from Terre Haute and think the only time I had to use 5th was in the 55 mph zones. Definitely pretty flat out that way and I was pulling 15k pounds. You probably wont even know your trailer is back there. Just take your time and drive however you are most comfortable with. Stopping is always whats on my mind when towing.

- - - Updated - - -

I need to add keeping an eye on your gauges, EGT and ECT mainly. I made my last trip thru the Blue Ridge mountains with my Banks tuner removed and it did behave differently. The tuner protected me from higher temps and I noticed I had to watch them more closely. If they started to climb I backed out a little to keep them under control. This was while crossing the mountains and the rest of the trip thru the foothills and flatlands was pretty normal.

I really don't see a need for the coolers unless your seeing dis-colored trans fluid well before its change time show that its broke down from heat. So if the fluid is stay clear colored for most of the way to 100k miles then you should be fine. At the worst you could install a trans temp gauge and see what's going on if your really concerned.

You has towing a 15k trailer and I am only Towing like 4k to 5k lbs trailer. That it... When I do towing, my cummins act like there is nothing. But I am caution as not go too fast or speeding for no reason. I only driving like grandma on my cummins so it will go far like twice distance Than my family's fleet vehicles do..

- - - Updated - - -

It is my first time to use my cummins to towing out of state. I just want to be prepare. But I will check the fluid to see what is color but it had changed two years as only like 10k miles. I know that I don't drive much but during winter time I had my cummins parked in garage as not worth to drive on ice or snow as county roads.

The NV4500 didn't like towing in 5th at low rpms due to the 5th gear nut issue, but AFIK the NV5600 has never had an official comment against towing in 6th. I tow in 6th when I am above 60-65 mph (1800+ rpms) and hold 6th until I start to slow or EGT's get too high (hot days at high elevation on steep grades). Nothing wrong with using 6th with decent rpms and your not slowing.I have fast coolers on mine, mainly for the added volume of fluid. The few threads I have seen on NV5600 temp show they can get a little warm on VERY hot days, but once fast coolers are installed it's not an issue. For a 5K lb trailer I wouldn't consider them even close to needed.Last time I towed a smaller trailer (7x14 enclosed, around 15-16K GCW) I used 6th 95% of the time. It was a tow from Bozeman to Seattle and I got over 14mpg at 60-70 the whole way. The only time I didn't use 6th was when the rpms were too low, I never had power/temp issues on that trip even on 6% grades at 65-70.

:iagree:I would have to agree with the above. Though I dont know much about the 5 speed. I had one for about 2.5 years but it was attached to a V10 gasser and would not pull the trailer in 5th except on flat ground.I do have a set of Fast coolers for mine but I cant find them. Whaa!! Whaa!! Whaa!!

I do have a set of Fast coolers for mine but I cant find them. Whaa!! Whaa!! Whaa!!

Did you look on your trans?

Did you look on your trans?

Aaaaaa, negative. Afraid to look now.