Better gas mileage and performance.

[L31MaxExpress]

If you're gonna go LS go 6.0,better torque.

Your truck is 4WD so you would want to change the gears in the front too.
It seems that gear ratio description has changed. People now say a 3.73 is lower than a 4.10 because the numbers of the 3.73 are lower. Us old graybeards would refer to the 4.10 being the lower gear and the 3.73 the taller one. Low gears(4.10's)will get you up to speed quicker and the engine will be turning faster at the same vehicle speed as the 3.73(taller)gear. The best scenario is to find the right gear that puts your engine in its torque range at cruise with the size tires you want to run.
The math is,
One mile(63360") divided by tire circumference = tire RPM. Tire circumference = tire diameter times Pi(3.1416)
Tire RPM times gear ratio = driveshaft RPM and engine RPM in direct drive.
Our OD trannys have a .7 ratio so you would multiply your driveshaft revs times .7 to get your engine speed in OD.
Lets say your tires are 34" in dia.
34" x 3.1416(Pi)=106.8"(circumference)
63,360(inches in a mile)/106.8=593.25(tire RPM)
593.25(TRPM)X 3.73(gear ratio)=2212.85(driveshaft RPM) and the engine RPM in direct drive @60 MPH
2212.85(DRPM) X .7(OD ratio) = 1549(engine RPM in OD) @60 MPH.
1550 is bogging your engine down with that tire and gear so to get the engine back up in the sweet spot you would want to lower the gear to 4.10.

Doing the math with a lower 4.10 gear brings your engine up to 1702 RPM in OD. Better but the sweet spot is 1800-2200 for your engine. That is where your going to get your best fuel economy and drivability.

Here in Texas, I do not find looking at RPM at 60 mph very useful. I shoot for 2,200-2,500 rpm @ 75-85 mph. A lot of our speed limits are 75+. The 2011 Pathfinder is actually right in that zone and it loves cruising 80-85 when speed limits allow for it. My 97 Express van is right there with a 4L85E, 3.73 gear and 30.5" tall tire. The 87 G20 is a bit shorter geared with the TH400, 3.08s and 29" tall tires. It turns about 2,500 rpm @ 70, however the cammed 350 Vortec loves to spin a bit. Yea we keep the hammer down pretty good in this state and it still takes hours to make it even halfway across the state.

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[Scooterwrench]

I was using miles per minute and revolutions per minute.
The divisor is 60mph(1MPM) so at 75 it's 1.25 MPM X 1550 with the current 3.73 gear. Still only puts him at 1938 RPM with 34"(guesstimated) of tire and then factor in the wind resistance and he's still at the edge of being bogged down. Remember,he's running a tired ol stock 305. It needs all the help it can get.

 

[L31MaxExpress]

I was using miles per minute and revolutions per minute.
The divisor is 60mph(1MPM) so at 75 it's 1.25 MPM X 1550 with the current 3.73 gear. Still only puts him at 1938 RPM with 34"(guesstimated) of tire and then factor in the wind resistance and he's still at the edge of being bogged down. Remember,he's running a tired ol stock 305. It needs all the help it can get.

My stock 305 had a 700r4, 3.08 gears and P225/75R15s as delivered from GM. Pulled the 5,300 lbs G20 fine down the road at highways speed, but look at a hill and it was in 3rd gear. I would have prefered 3.73s but that option box was not checked on the factory build sheet. Despite that, the tired 305 did just fine cruising at lower rpm. With the taller rear gear, it was not like it could not have hit 2nd at 65-70 mph if needed. I never found a driving situation that required getting into the secondaries and a 3-2 downshift unless it was passing quickly on a 2 lane road. That little 305 would go from 65-85 mph passing a semi if it needed to fairly quickly.

 

[Scooterwrench]

That little 305 would go from 65-85 mph passing a semi if it needed to fairly quickly.

Mine must be really tired. It struggles to get over 80.

 

[L31MaxExpress]

Mine must be really tired. It struggles to get over 80.

Must be, even with 200K on mine and pushing a brick, it would run triple digits without too much persuasion. I had been through the Q-Jet and recurved the HEI which pepped it right up, so not completely stock at the time but close. I feel like this was prior to the Thorleys Tri-Ys and Performer RPM manifold going on but the video is so old, I forget if it had them or not. It was definitely still stock cam though at the time. The cam I had in it later was the old Crane 274H06, it had a fairly choppy idle to it being on a 106 LSA. It could have benifited from a better rear gear and definitely was not winning any 60' races, but it still had decent get up and go for what it was.

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[Scooterwrench]

I'm still running iron logs and restrictive factory exhaust minus the cat. I may need to turn my fuel pressure up to 12psi.

 

[L31MaxExpress]

I will take your word for it but I am surprised. How does the computer keep the engine at 14.7ish without the input from the 02 sensors?

The computer is programmed to run the engine close to 14.7:1 without the need for 02s. For startup, initial warmup, WOT as well as Lean Cruise where GM used it the computer is running off the MAP sensor via the programmed VE table and the MAF sensor. In the newer Vortec PCMs, there are also a lot of complex density and predicted airflow compensations going on that use Barometric Pressure which comes from the MAP sensor and gets updated at lower rpm when the TPS is well above idle in normal driving, IAT, CTS and TPS data to help establish.

 

[L31MaxExpress]

I'm still running iron logs and restrictive factory exhaust minus the cat. I may need to turn my fuel pressure up to 12psi.

13-14 is the sweet spot most like.

 

[PlayingWithTBI]

I may need to turn my fuel pressure up to 12psi.

"Up to 12"? Why so low?

 

[PlayingWithTBI]

13-14 is the sweet spot most like.

You beat me to it, ha ha!