Right now my blazers mildly lifted, with 31" tires, and has 3.42 gearing. I'm going to eventually lift it more, but as of right now, my blazer feels kind of sluggish and is getting not so good highway gas mileage. So I was debating on swapping rear axle, or plain out just swapping in gears, what should I do, what should I change to? 4.10's? 4.52's? Other? Please help me out here.

 

Pardon me if I'm mistaken, but going up in gear size, i.e 3.73 to 4.10 would make it worse for gas miliage wouldn't it. I'm pretty sure that's what happened when I went from 2.73 to 3.42 to 3.73.

 

For Gas Mileage.... you want a smaller gear... like 2.73 as stated above... it will give better cruising rpms

For quick acceleration and less "slug" go with a bigger gear like 4.10 and 4.56....

 

Yeah I definitely noticed a difference in my acceleration with my 3.73s. Also you'll run higher RPMs with higher gears, and you'll Speedo will be off, got pulled for 65 in a 45 because of that, no ticket tho... lol

Anyway, have fun with a gear swap lol. I had to change the entire rearend because of what I did to them. I'm sure a plain gear swap is much easier.

 

If you do end up doing a gear swap... drop in the posi traction rear end...

 

Ok I understand better now, tnx, I think I might switch to the 3.73, and use a zr2 rear end, I think that will be a happy medium. A little less acceleration and a little lower highway rpms. Correct me if im wrong, wouldnt lower gears raise highway rpms and higher gears lower highways rpms?

 

Correct. 'Lower' means a larger number (ie. 4.10) and 'taller' means a smaller number (ie. 3.08)

 

I also have 31" tires and 3:42 gears. I am planning to go to 4:11s.
Right now the 3:42s are just to high and at 75mph my tranny will just not stay in overdrive on the highway when hitting a slight grade or even a strong headwind.
Installing a higher gear like a 3:08 will not give me better gas mileage because the engine will not be in it's happy area. (That's a dealer term, look it up)
With 4:11s, the engine will not have to work as hard, but the trick will be to keep my right foot off the floor and the speeds down to salvage the gas mileage.

 

what size tires do you plan on going with. I have 33x1250s with 3.42s. I dont think its that bad. They suck on the highway but for city driving i dont have a problem. I may not be able to spin the tires on dry pavement but it still takes off fairly quick. Im also thinking about getting a ZR2 rearend though. there are a lot more options for lockers.

 

I am gonna stick with my 31x10.50s for now but like you said, it sucks on the highway... and most of my driving is on the highway. I also pull a 1300lb trailer on occasion.
If I am gonna go through the trouble of re-gearing both diffs, I am going with 4:11s... If it's too low I can always install more lift and taller tires!