Best rear gear for a 4.8, 265/70/17 tires?

[BLACK DEATH]

Ok so my 01 truck has a 4.8, 3.42 gears and currently 265/70/17 tires.

It initially came with 235/75/16 tires.

My concern is that when driving on the freeway is that it feels it is lugging being lower rpms with 3.42 gears & the taller bigger tires. I guess with stock tires it probably wasn't too bad. It does kick out of over drive also when going 70-75 with the cruise control on when going up hills.

So my question is, 3.42 & these taller tires are lowering the rpms but do you think it is hurting me more on city & freeway driving with mpgs?

I know 3.73 gears aren't much difference vs 3.42s but I have a complete rearend from a Tahoe that I can swap the posi & gears out of into mine. Ill do the work myself as I've done it before on other vehicles so that's not another issue.

Would the 3.73 help more even though the rpms will rise a bit?

I also have hptuners for anything else I need to do to it after the gear swap & ill do the correct circumference for the tires so it will all be correct.

Sometimes trucks seem to do better with more gear.

Any other input wether bad or good I'd like to hear.

Bring anything to this table you'd like to say or know.

[Chris]

I had that setup with 265/75R16 and 275/55R20. It was tubed and i drove it cross country a couple times. Never noticed it being really weak. I wouldnt go through the effort unless you had a 4.10

[WilliamBos]

My 2011 has that exact combo from the factory, works just fine. I had 3:73 in my 04, miss that ratio for towing.

[BLACK DEATH]

Do most 4.8 trucks come with 3.42 gears?

We have an 03 truck same setup per rpo codes but the rpms are higher on the freeway compared to my truck.

It gets good fuel economy for a truck and pulls good on the freeway at light throttle.

It seems it has 3.73 or 4.10s which makes It snappier

[kstruckcountry]

I believe code GT4 is 3.73's.

[dard6555]

Your change in tire size was about 9% increase in diameter. The 235's should have run about 1960rpm at 70mph in overdrive. Going to the 265's the engine is going to turn 1770rpm at 70 and 1540rpm at 60. This could be a little low in the rev range to get the truck moving without stepping on it quite a bit. If you changed to 3.73 gears, which would be a 9% change, you would be back up to 1940rpm at 70 mph. Stepping to a 4.10 gear would be a 20% change and would spin the engine at 2150 at 70mph. This number might be acceptable for performance but gas mileage may suffer.

[KMGZ400]

I had a 03 4.8 (which even had a little more HP then the 01 4.8) with 3.73s and it still dropped out of 4th a lot during normal highway driving. Did it with the 265's and got a little worse when I leveled it on 285's. You'd be better off saving the money for a new truck rather then dumping money into an 01 for a gear swap. IMO

[BLACK DEATH]

It has a gu6 rpo code in mine and the 03 work truck.

The rpms at 70 are just higher on the 03 work truck compared to my 01.

Dard, that's what I was thinking that 3.73 would bring the rpms up a bit.

It seems the taller tires lower the rpms and its a turd or is to me.

 

The reason I ask about the gear swap is that I have a complete 3.73 rearend for free from an escalade.

I can use the gears and posi and do it myself so its very little money to do this swap.

I know the truck is older but it still a good truck.

[Stevens03]

3.73 is a great gear for the 4-speed trans but I can tell you that 4.10s are better all around and you can still achieve good mileage.

[BLACK DEATH]

Wish I have 4.10 gears already for it but only have 3.73 gm gears so they'll be quiet.

Anyone know what all trucks came with 4.10s in an 8.5/6 rearend?