I've got the 3.55's and am yet to decide how well I like them. They are pretty decent on highway but when I compare it to my Tundra, the 390ish hp doesn't feel quite that potent because 1st is such a long gear. I think mine does 50mph in first gear. I think 80 mph is about 1800 rpm though so that's great for highway.

 

I also have no issue getting 15ish in the city if I drive it right, all about MDS kicking in and staying on as long as possible. My secret is using cruise control even in 35 zones. Of course traffic dictates that, it is not bad where I live.

As for gear ratios, it is the final ratio that really matters, especially when you want MDS running as long as possible.

I am a believer that if you have the 20s the 3.92s are right for this truck and the 17s 3.55s are fine.

Why do I say final ratio? If you have 3.92s in a truck with stock 20s on it and you decide to "rice it out" and put on 17s with next to no rubber (ie small diameter tire vs the stock 33" tire) your MPG will go down even though you did not touch that gear ratio. With that setup your final ratio will have changed quite a bit.

You will see people who go big on tires will put 4.10, 4.56, ect, this is due to the massive rotational mass of the tires, the taller gears help to offset that and keep the acceleration "seat of the pants" feel, again, final ratio.

This article explains it a little.
http://www.chevyhiperformance.com/te...ing/index.html

 

The 3.55 is a decent gear. I have no idea how it would perform in a 4x4 since it doesn't have LSD. I'm not sure what kind of off-roading you're looking at doing, but if it's anything other than going down fire trails, then I'd go with the 3.92. I've driven both the 3.92 in a test truck I had for a number of days, and then the 3.55 in the one I bought. With the 3.55 the kick in the pants just really isn't there. With 390hp it's got some get up and go, but you really feel like the truck is the full size truck that it is. The 3.92 really makes it feel sporty when you give it a little gas.

I'm eventually going to put 4.10 in mine. All I need to do is save up the cash first. Of course to do that I need to stop all these things that keep coming up that keep sucking the bank account dry.

 

By hand (Evic reads higher I think, although I do not check it regularly). I do not use premium, but I do run 100% gas (there are a few stations around here that use no ethanol, and that could be helping a little).

 

How is that possible? How is your truck equipped?

 

Aren't you suppose to run a higher octane. In my county there are NO 100% pure gasoline stations.

 

What is EVIC

 

Electronic vehicle information center.

That big digital thing in the gauge cluster, if your truck is equipped that way.

 

I have the 3.92 rear end and am very pleased with it. I am getting around 22 mpg (imperial gallon) on the highway and 17.5 (imp.gal.) in town driving. My last 2 trucks were F-150's and they never saw more than 20.5 / 16.5. My dodge isn't nearly broken in yet so I am very happy and I would reccommend the 3.92.

 

Hey do you wish you had at least 392's or even 456"s, I hate the sluggish pull, makes ya wonder if it is really 390 hp