Yeah the 87 Tune is pretty awesome as well! It still makes the tuner worth it, IMO!

 

Actually, 3.92's or 4.10's would be good for low end power. The 3.55's are more of a "highway" gear (lower RPM at higher speed). With my 3.55's, the 4.7L and 265x60x18's I turn 1916'ish RPM at 70 MPH. If I had 4.10's I'd be turning around 2213'ish RPM. So with those 3.55's you are losing a little low end grunt as compared to a 3.92 or 4.10. The 3.55's would return better fuel mileage on a long flat stretch of highway than the 3.92's or 4.10's.

Because I live above 5000 feet and hit a lot of big hills I wish I would have gone with the 3.92's. The engine just bogs way to much with these 3.55's and my gas mileage suffers. To get most of the mpg back I run around in tow/haul mode until I hit 75mph.

 

I would be interested to see what a set of 3.92s would do to my truck. Im just not to sure about doing 2200rpm doing 70. Thats a little high. Either way, I dont think I want to spend $1500 to find out.

 

I wouldn't spend the money to go 3.55 to 3.92 but definately to 4.10s. My highway RPMs aren't bad at all but I'm two wheel drive. 4.10s will certainly get you out of the hole alot faster.

 

Yeah, it sucks having to do both diffs with 4wd. Otherwise I would definetly consider it.

 

Went from 3.92 on my stock 4.7 HO "J" engine 4x4 to 4.10 front and rear. (My truck weight with gear and a full tank and me in it = 5,200lbs...total weight with trailer = 9,460 per CAT scale which is 80% of max combined weight rating). Kept OEM 30.6" tires.

Did this for towing a 4,200 lb travel trailer in the mountains and with headwinds out west.

It is now the perfect set up. Seldom does it downshift out of overdrive on gentle grades at 65mph (1950rpm) and I'm able to maintain 55mph (1900rpm) on 6% grades in 4th gear or at worst 3rd gear (2500rpm). Before the gear swap it was common to drop down to 2nd gear on those grades and barely maintain 45mph (3300rpm). On hot days over 90 deg. the coolant temp would rapidly increase to about 3/4 scale where the fan clutch locked up, robbing me of about 15HP WOT and further reducing performance as well as economy. That doesn't happen anymore. (I also installed an aux tranny cooler with a diverter shroud to route the heat down below the radiator and into the slip stream)

With 15mph plus headwinds there were times that I had trouble maintaining 50mph in 3rd gear with the 3.92 gears. Now I'm able to maintain 55mph plus in 4th gear under those conditions.

Also, my average MPG increased about 25% while towing (12.5 vs 10mpg) This significantly increased my range between fill ups on I-10 in west Texas, New Mexico, Arizona where one can get stranded between service stations if wind conditions are unfavorable.

In city driving not towing my MPG increased about 10%. Highway MPG not towing at 70MPH dropped about 8%.

I recently bought a Superchips Cortex tuner and the performance increase with towing tune and 93 octane is significant in the 1800 to 2500RPM range. Can't wait to see how it cruises at 55 to 70MPH with that tune.

You may well ask: "Why not buy a hemi Ram?". Well, I did that (December 2009 and only because the discounts on the ram made it CHEAPER than a new Dakota) and here's the dirty little secret. The HP/Torque curves on the 4.7 in the 1800 to 2500RPM range ARE HIGHER THAN THE HEMI. You can look it up here. http://www.dodge.com/en/2010/ram_150...ty/powertrain/

I'm waiting till after the first oil change on the Ram to test it's towing performance but all the guys on the Ram forum claim to get no better performance or economy at the 9,500lb total weight range and 3.92 gears than I get with the Dakota.

I may end up selling the Ram (even though it is far superior in ride comfort and features) and keeping the Dakota.

 

Hey 05Dakotaho, your towing requirements are very close to mine. My Flashpaq arrived yesterday and I am planning on upgrading to 3.92 gears. I am in N. Texas. Maybe we could communicate directly as I am trying to decide if 4.10 gears are a better way for me to go.

 

You betcha. I sent you a PM.

 

WOW... with all the tuner talk it sounds like a great upgrade!

Where are you guys buying them (it?) from?

BDG

 

this is what hemifever told me about the octane question.

well the tunes can be worked based on the octane. I can lower timing and find a good spot that will work with whatever octane you get. 93 octane will have the best performance. The lower the octane the less of a performance increase you will get. 90 and 91 should be pretty similar. 180 tstat and plenum gasket fix for sure. maybe a cooler spark plug too. The least engine load the better. efan and u/d pulley for starters. 4.10 to 4.56 gears