3.5 gears would be perfect for 33's. I run 4.10's with 38's. I will probably swap in 4.56's some day, but with 4.56 and 33's your highway RPM would be way too high. If you will go to 35's some day then put in 4.10s now. If 33's as big as you will ever go then get something around 3.5.
I have nice big V6 with stock 3.42s and 33 MTs annndd...its not low enough by any means. 4.11s at minimum but i would be tempted to go with 4.56s if you dont drive on the highway too much and take it offroad a good bit. Otherwise, go with 4.11s for sure.