If I towed a lot more often and didn't drive so much highway, I would have gotten 4.88s. The difference isn't as much as people think, but on long highway stretches at higher speeds it would run me around 2400-2500 rpm cruising which is too high.

 

I'm curious what your RPMs are at highway speed, my commute to work is mostly interstate and my normal speed is 75-80. I'm thinking it's going to be one of those you can't have your cake and eat it too situations.

 

Here's a calculator for you:

http://4lo.com/calc/gearratio.php

 

I wish I knew where to find all the info to fill out the chart

 

2150 @ 70mph. About 2300-2350 @ 80mph.

 

Yep, the EDGE shows ~2250-2300 @ 75mph. I was just about 1850 with the 3.73s. For the guys with questions, it's important to note that although the RPMs are higher at freeway speeds, the truck's powerband feels perfect for all around driving, especially around town, driving up grades, passing, etc. Towing should be a dream come this Spring.

 

just out of curiosity are your guys's 35 inch tires actually 35 inches? I've heard some guys say their 305s are 35s and mine aren't even 34, just curious .

 

The chart is a guide as it does not calculate overdrive. But the differences in RPMs @ 65/70mph are just about right.

 

I've done this mod a couple of times. I started out with 3.55's stock, but with 35"x14.50" Nitto MG's I needed something different. I put 4.10's in and averaged 17 mpgs with my 4.6L (the 5.4 may not get that good). Switched to 37"x12.50" Iroks and switched gears to 4.56 with detroit truetrac and was able to cut tight donuts on dry pavement. Fuel mileage didn't change much, dropped about 1 mpg. I drive my truck everyday, so fuel mileage is important, if not then I would've went with 4.88's just to have the better towing power.

For what it's worth, definitely worth the money to re-gear your truck if you run oversized tires!

 

My 35x12.50r18 KM2s are 34.8" tires according to BFG. Go to your tire manufacturer's website and you can look up the exact diameter.

305/60/18 tire is about a 32.4" tire, and a 305/55/20 tire is about a 33.4" tire. It all depends on the aspect ratio and rim diameter.

 

Should be pretty self-explanatory - transmission ratio is 0.7 in overdrive, transfer case ratio is 1.0, then you fill in 3 of the 4 others (tire diameter, RPM, MPH, gear ratio) and calculate.

 

That calculator says that 4.56s with my 33.5" bf at 1920 at 60.....not in od. That doesn't sound too bad for me when it drops a few hundred rpm when it goes into od.

 

That definitely wrong. mine turns nearly that RPM at 60mph with 35s in OD.

 

Glad to hear your happy with the gears.
Just got mine done 6 days ago and have rolled 400 miles on them. Im running 37x14 iroks and 4.88 LS. The difference from 3.55 is much more than expected. I just had to try to spin the big super swampers and she did it at 1/2 -3/4 throttle. I run around 2000rpm at 55mph (speed limit is 55 round these parts and I take it easy on the road, save the beating for offroad). Big props to wayne at diffsonly, ill only shop there from now on.
My only gripes with the install is that the ring had to be ground down to fit the center pin, and the yukon pinion threads don't run as far as the stock pinion threads so I had to make my own spacer to take up the slack.
And one more, I WISH I HAD GOT 5.13s!!!
can't wait to try out some crawling in 4low. As before I had to use 4low all the time, 4high just wouldn't cut it!

 

Here is a very rough and quick graph shwing the rpms versus gears and tire. This takes into account squish. Sizes 265-70-17, 285-70-17, and 315-70-17. Also .70 overdrive. 70 mph.