I was towing my 11K 5th wheel over the new years holiday and decided to drop into 5th gear instead of 6th. I was use to towing with my 04 4 speed auto which seldom down shifted but with the 68RFE it started down shifting more often. I was towing on I10 between San Antonio and Houston which has some small grades and there was probably a little head wind. But I decided to try 5th gear and with the 3.73 it was running around 2200-2500 RPM's and the mileage seemed a little better. Is the 6 speed going to shift more than the 4 speed? How many of you tow heavy 13-15K with the 3.73 and are you happy with the performance? Thanks

 

the 68rfe has 2 overdrives as i understand. what were your crusing rpms in 6th and what was your boost #s?

thats a boring drive btw

brett

 

Brett, at 70mph the RPM's are about 1800 if believe in 6th gear. I don't have an gauges and I know most do around here, but after paying for this truck every month the wife said no more $$$ for me. Most drives in Texas are boring.

Thanks
Gavin

 

where are you from?

brett

 

I would think towing at 2200-2300 would be fine and you would still get good fuel mileage. My truck would turn about 2250 @ 70 before I switched to a little taller tires. I know my truck (even though it is a 5.9) likes to be up around 1900-2100 for pulling in the hills, if it is lower than that, it will lug and require a downshift and that sounds about like what you were getting. Seems like the truck is doing what it is supposed to. Heck towing in 5th with alot of weight seems to be fine also. Seems like you would get great mileage while empty also. Scotty

 

your rpms should be a little over 1600 when going 70 in 6th gear.i just leave mine in 5th when im towing puts me right at 2000 rpms like my ole 48re but if i wanted to tow in 6th i would have to go 95 so the rpms would be up high enough so it doesnt downshift all the time lol

 

Well all these GURUS that want 3.42 say OH that gearing and those RPMs aren't needed.Let the TURBO work and not the gear.Some comment that THEY pulled 15k to 20k with the older trucks and 3.55s. I say BUNK! I like my 4.10s and NV5600 pulling 10k plus at 68/70 mph.

 

Hounddog,
Have to remember the 3.42 is only available with the G56. So in overdrive the rpms should be very close to the 6spd auto OD with 3.73's.

MikeyB

 

Cummins says not to have a large load on the engine below peak tq rpm... so be sure to stay above that... otherwise boost, egt, and fuel mpgs will tell you what you need to run.. On the 5.9 2200 seems to be the sweet spot (stock) and anything above 2500 runs real high EGT's... have yet to see if the sweet spot changed with my smarty on 40hp...

 

Those guys must be the ones that have to throw out the parachute to stop!!!!! LOL Only way I see that possible is to have the RPM's up and that means higher speeds well over the speed limit.

 

If your towing more than 14000lbs, you'll find that 65mph at 2250 rpm's can't be beat for mileage and power without down shifting. (6 speed) As mentioned above Cummins recommends you gear the truck when towing to stay in that RPM range.

My Son's in law did a 16,000 mile trip to Alaska towing a 16,500lb Carriage Fiver and averaged 12.6. six speed and 4:10 combo, 2005 Dodge 3500.

Dave

 

brett, I'm from Boerne.

Thanks for all the replies this info really helps.