I,m also have a 6.2 Diesel,with 33" tires and the stock 3.08 and now i,m working on a 79´12 bolts axle to install on it.The gears i,m mounting are 4.10.
We have to pass a Technical inspection every six months here in Spain.
I didn,t make my 33s legal so i have to mount the factory 235/75R15 6.2 Diesel stuff for those inspections.
Well,when i drive with those original wheels the truck does run a lot better than the 33s.It sucks ,looks like a Vespa motorcycle but does run like a cat.
What i mean is that in the end is a simple mathematic rule:
If i go ok with 235/75r15(28.8") and 3.08 ratio
with 33" i will need x ratio
x=(33 x 3.08)/ 28.8 = 3.52 ratio
3.52 is pretty close to 3.73 wich is in the ballpark,but just like Sweet K30 said before,you will want to go a bit deeper that you think you need to go, so 4.10 is your number.
Just my 2 cents