Hey, I'm looking for a recommendation on gear ratio. The truck is a 2wd '06 rcsb 4.8, 70mm turbo, 3.23 gears with a 315/60 (29.9") tall tire. I haven't ran the 1/4 mile yet but in the 1/8th mile it never even got out of 2nd gear at 95 mph. That was with a 4l60e and a 4000 stall.
I'm currently in the middle of installing a 4l80e and a new FTI 3600 converter. I also plan on switching to a s475.
I'm thinking a 3.73 or 3.42 might be a better option with the 80e and 3600 stall? Any suggestions? Thank you

 

I've got a similar setup to yours, and after a ton of research, it seems 3.90 or 4.10 is the best with the 80e gearing

 

I had a 28.7” tire (315/35/20) with 4:10 gears. On the highway it turned close to 3000 at 80, was a little high for me. Also, it would only downshift to second below 60 which kind of sucked. That may be able to be changed with a trans tune... not sure. I’ve since changed to a 9” with 3.70 gears, I’ll let you know how that goes. Should be back on the road in a few weeks.

 

3.73 would be the minimum I would go with, 4.10 if you can tolerate it taching higher on the interstate.

 

My Denali has 4.10s and is very snappy off the line and I like it. I never would have guessed anyone would say 4.10s in a turbo truck but I like it. I think that's what I'll try. Thank you

 

The smaller the motor, the more RPM the turbo likes to help it spool. Don't fear the gear!!

 

with a 316/60 there is no doubt in my mind you should be running a 4.10 gear.

 

Just ordered myself some 4.10s

 

^^^
This right here, I was running 4:56’s with my setup on both the turbo 4.8/6.0 with same tire. Was an animal off the line.
Currently swapped to 3:73’s now as I’m going to be shooting for 1k rwhp

 

It's odd because almost every search I did ended up with people saying something in the low 3.XX ratio so you can load the turbo or some ****. Maybe on a light car but I definitely agree with the 4.10 for heavy trucks.