3.73 work great with 33" tires. Just like stock
Setup. But taller tires, speedometer is also correct I know because I ran that ratio for a while b 4 going to 33"s

 

Sounds good looks like I'm going to running 3.73

 

get some pictures...we love them

 

I will I have stock well how my truck is now pics of it just sitting and flexing jus I'm always on my iPhone on the sit and can't upload pics directly

 

Xillxnickx.... hold up I fu on the last post. I hit 33" instead of 31" sorry bout that.... 33" tires are sluggish and you will teduce you gas milage to 22-13 mpg... a gear change must be done to run 33" The last post is for running 31" tires.... sorry bout the mix up.....

 

Xillxnickx... im currently running 33" with 3.73 gears and gas milage sucks, acceleration sucks and the slightest incline on the hiway it shifts in and out of overdrive... I do have a set of 4.56's waiting to be installed. Just need some money....

 

Xillxnickx, I'm running 32's with 3.73 gears and I wish I had 4.10's. I wish I had just a little more low end torque for accelerating and off-road. Crusing on the highway at 65mph my engine runs at 1700rpm in OD, which is pretty good for highway fuel economy though. I get around 17-18mpg as long as I can keep my foot off the skinny. I'm really surprised that you're around 2000rpm with 3.42 gears and 31's. In my experience 3.73 gears are well matched to 31's in the Blazers, but if you're going bigger than 31" I'm with okiedoak20 and think you may want to consider lower gears, especially if you off-road much.

 

Ok I'm lost on what ratio to pick I'm an manual not an auto so I'm guessing we have some difference with the ratio coming out the tail shaft

So for a fact 60 mph I'm doing 2,000 on the dot
5 th gear doing 40 I'm at like 1,200 1,300 I can't remember perfectly and I know an auto at 40 should be right on 1,000 if I'm right

Honestly I love my 3.42 I have no low end power problems or problems off roading but I've only been on the beach haven't gone mudding sence my old truck plus it's illegal here .... But I'm worried that with all the extra weight from the swap will slug me down I guess I will just do the swap and see how the 3.42 gears are I don't plan on going to 33 for about 20,000 miles or how ever long these tires last

 

I'm also a 2 door I don't know how much of a difference it makes to a 4 door it weight I know my truck stock weights 3,300 about

 

In my Blazer over the years:
3.42 w/28" = stock, great
3.42 w/31" = good
3.42 w/33" = worked, but not ideal
4.56 w/33" = great
4.88 w/35" = great