How much of a gain will I see in the 1/4 mile switching out my 3.42s to 3.90s. And where is the cheapest place to buy gears. Thanks.

 

well first ? about 3to4/10 and second ? look on ebay they have some good prices there for new stuff

 

These guys have great prices and service....
http://www.gearsareus.com/
http://www.ringpinion.com/

 

I would go to 4.10's or better in a big heavy 5000lb plus truck like that and not waste time with bastard 3.90 gearing (very few vendors make it so quality of choice is limited). A 5.3 is not that torqey but it likes to rev. You do have OD so 4.10 in no where near as bad as it sounds. 4.10 should knock 1/2 to 3/4 or a second off on it if you get a good launch and a 4.56's should give you close to a second because you are dragging a anchor now with present gearing

 

.2-.3 gain is what i'd expect.

 

Snowman I would go with 4.10s but I do like to take my 2wd 4400 lb truck on trips lots of highway driving I am sure those couple of hundred rpm mean alot in the 1/4 as well as the highway. I figure 3.73 for street 4.10s racing =3.90

 

I like mine. I have "Strange" gears, and no problems.

 

Yes but you are forgeting OD which is .7 and it knocks that 4.10 down to a effective 2.87 in OD which is pretty tall for a truck that has 31's or better on it and should yeild about 1900 to 2000 RPM at 60 and around 2300 at 70mph which that 5.3 would loaf at and be closer to its torque peak and engine deliver their best MPG when ruising at or near torque peak. I understan your logic about the 3.90 but the limited selection of 3.90 gear sets put limits on quailty too. I remember driving croos country many year ago in a 4x4 P/U with 4.10's and no OD. I remember cruising at 3200rpm and better sometimes and averaged about 15 MPG on those trips which was great for that old big truck. some extra RPM does not hurt a engine nor does shorten its life as some claim (lugging a engine too much under a load can actually shorten its life) and it reduces the piston/ring/bearing loads at a the same HP level as it take more pressure and strain to produce say 80HP at 1800 RPM than it does at 2300 RPM.

 

With my current mods(n20 excluded) when I went from the 3.42 to a 4.10 gear with open diff(traction isnt a problem!) I shaved 4 tenths(.4) of my 1/4 mile and that was with my shift points and all that getting changed. Your gonna get the 3.90s and say why did I wast my money on these I should have gotten the 4.10's. Trust me on this after I got mine I wandered what 4.56's would be like and wanted more!

Oh yeah I have Strange gears(us gears)

 

I can get the 3.90 gears made by Srange gears (US gears) Richmond has them as well. Alot of places where the speed limit is 75 you gotta go 85 to keep from getting run over. I beleive Id be around 2600 rpm with the 3.90s at 85 mph my factory stock tires are 29" tall. Youre not gonna change my mind. Thanks