From 3.23 to 4.56 gears
 

My 05 4.8 L 4 L 60 e Sierra has 305 / 35 r24s with cold air intake and full exhaust and Hypertech programmer at the moment. Will be putting ported intake, 3200 stall, custom Tunes and gears. My 3.23 rear end isn't cutting it for the big wheels. Thinking about putting 4.56 gears but want to make sure that it's will be a good combo before spending the money

4.56 at a minimum

at the minimum? What would be good above 4.56? I thought 4.56 was pushing it

from what i understand, going lower than 4.88 in a 10bolt gets dicey & you're better off swapping to a 14bolt for 5.13 or lower...
however 4.56 should be fine & will be a marked difference to that little 4.8 with those heavy 32" wheels/tires. i've got 4.30s with my 33s, and the highway RPMs are just above where i'd ideally prefer them, but i've also got a stick shift (autos are better with turning faster).

What transmission. My next big mod for my cammed L86 with a 6L80e will be gears since I run 22x12 33" tire. I was thinking 4.11s but would like 4.30 if I could find them for my truck. It runs good with the stock 3.42's on this newer engine. Thats why I think 4.11's might be ok.

I have a 2011 Chevrolet Silverado it has a tsp stage 3 cam with 110lsa, has aftermarket heads , lomgtubes,2800 stall. It had 3.08 gears, but switched out to 4.30 gears with the detroit tru trac diff. Has the 6l80e tranny. I run 20x12 with 33 inch tires. I can crusie the interstate at 80 mph. Rpm right at 2150. I would go with 4.56 or 4.88 if i had to do it over again. I also pull my 6500lb camper with this setup.

I run 5.38s with 36"s, I also drive around with 33" slicks on sometimes. Dont fear the gear

I would rather run 4.30's but I don't think you can get them for my truck.

why not? i'm running 4.30s in mine. stock 1/2 ton diffs