What I am saying is the best power and mileage with a 31" tire would be to use the 3.92 gearing. If you are running 3.55 gearing it is harder on the engine and that you would most likely get lesser fuel mileage and power.


For instance, I have 3.55 gearing in mine with 33" tires (285x75x16's) and with that it's WAY to high geared and killing my with mileage. To offset concitering the truck with the 3.55 gearing was to push a 245 tire. So if you do the math with the 33" tire being oversized over OEM 245 tire that makes the gearing more like 3.23's and not 3.55's. This kills my torque and my mileage. Also this puts my motor in a "lugging" RPM and makes it work really hard.

So to offset the 33" tire size and get more torque a larger gearing is needed. I am going to 4.10's here in the next month for that. With my offset gearing and tire size it will be like re-gearing to a 3.78 and 245 tires which is the perfect medium for everything. Towing will be easier on the truck, better RPM range for more efficient fuel mileage and also torque to the rear. Basically the best all around, however with a carrier break at 4.10 the largest I can go is 4.10 and I want to keep my carrier because it's a Limited Slip. If it was open gearing I would build it differently. But overall I have thought about this for a year and have made my mind up. I can't even light up the tires, however with a 4.10 I could light up a 44" tire. Big difference huh?

So, do you see where I am coming from? 31" tire with 3.55's isn't the best match up. The best match up for a 3.55 is a 235, and a 31" tire is the 3.92's.

 

im not sure about the total gear ratio in my truck, but i have 31's, w/ the 3.55 rear end in it, however i also have the 545 (5 speed) transmission. and i have not seen anyone on this forum who gets better mileage w/ one of these trucks than i do (i can pull 20mpg if i behave on the highway)

 

Transmission Gear Ratios

GEAR RATIOS
The 45RFE gear ratios are:
1st . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.00:1
2nd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.67:1
2nd Prime . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.50:1
3rd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00:1
4th . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.75:1
Reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.00:1


The 545RFE gear ratios are:
1st . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.00:1
2nd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.67:1
2nd Prime . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.50:1
3rd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00:1
4th . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.75:1
5th . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.67:1
Reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.00:1


46RE
TRANSMISSION GEAR RATIOS
46RE gear ratios are:
² 2.45:1 (first gear)
² 1.45:1 (second gear)
² 1.00:1 (third gear)
² 0.69:1 (forth gear)
² 2.21 (reverse)

42-44RE
Gear ratios are:
² 1st 2.74:1
² 2nd 1.54:1
² 3rd 1.00:1
² 4th 0.69:1
² Rev. 2.21

Well as you can see the gear ratio's are different, and that equals different overall ratios. From what I understand all the transfer cases are the same 1.1 ratio and therefore wouldn't change anything unless it was AWD because you push the front gearing. Anyway you (Sharps) having a 545RFE is different then most everyone else that has a 45RFE or 42-46RE models. You have different gearing and a extra gear, this is most likely why because rear end ratio's end up different through out the entire shifting and MPH ranges.

In my ratio's (which are different I know) it is over the extreme mark and need to be changed. 3.55's were installed mainly for more fuel mileage and not for people who tow a lot. Most customers don't know the difference and they look to the sells man to ensure they get the correct packages for what they are planing to do with the truck. Problem is they only want to line their pockets with cash off the deal so they tell them anything to sell the truck. If someone has more cash up front then they know to throw more at them, that the reason they ask how much of a payment they want to stay with up front......LOL.....Bastards

Anyway, again because of your extra gearing and differences in those gears you get better fuel mileage, not to mention you know your truck and how to work on it.

 

lol i figured the extra gear was a big part of it, but i didnt have the list of ratios to confirm (i kinda thought it was geared alot differently), and yes taking care of the beast helps alot too im sure. gonna be doing the 100k service this spring i think (more than likely it will be done at 98 or 99k)

 

Not trying to hijacking the thread, but is that a standard transmission?

 

it was the transmission behind the 4.7 in the 2003 model year, however they did make the switch very late in the 2002 model year, my truck was actually a floor model for a new color they were selling on the 2003 trucks, so i got one of the last 2002s manufactured

in the case of your truck you would have gotten a 4 speed because you have the 5.9, but this was not the standard transmission for your model year either.

 

Tire weight makes a significant difference also

 

I think the answer he was looking for is more along the line of no it is an automatic. I think by standard he means manual.

 

o, i took it to mean standard equipment, lol my bad, either way the answer is no

 

My D has been running 31x10.5R15s on the stock rims ever since we got it. (98, 5.9, 3.92 gears) No problems whatsoever, and the speedo is accurate within 1 or 2 mph at highway speed as double checked against both of my gps units. (Garmin Nuvi and an HTC Hero Android phone)