Its an 07 so its a 60e.65e.70e combo.
In honest opnion...best advice i can give you... Change the trans to a 80e very soon bc that trans you have now will hate you worse and worse as life goes on in front of those tires.


If it was me id do a 6L90e swap with 4:10s and never look back. Then if you supercharge it you have plenty of trans and gear to help you move. A tq style cam and a tvs1900 ontop of the 5.3 with some cleaned up heads will be very nice even if you stay stock manifolds

 

4L60e

 

Do you know what gear you have now? If not look in the glove box and look for the gear ratio code. The 07 generally would have come with a GU6 3:42, GS3 3:73 if it has a tow package and they even put 4:10s in the 6.0 with a tow package GW8. I am assuming you have a 5.3 because the 6.0 is kind of rare. I would agree a 4:56 would be a good choice with 34s and a 4 speed. This would be your best bang for your buck mod.

 

I have 4.56s and a 34" tire by far the best mod ive ever done. I used USA standard gears from rons machine shop. Ive had them for about 1500 miles now (knock on wood) but there holding very well. Plus my hwy mpg at 80 went from 11 to 13 give are take

 

USA gear are good products. I've had far better results using them in many gear swap's we've done than some other name brand products. Motive is my next favorite. Their machining tolerances are very good and the initial setup on them is almost as easy as OE gm gears.