3.90 it is, when the 3 speed OD became optional they came with the 4.11 and did pretty good on the highway while still being able to haul a load, you'd never use the OD with a 3.08 and likely be frustrated with having to slip the clutch to get rolling
not sure with it being a GMC, but the only other possibility would be the 3.55 gear set Patricks offers, which some folks use instead of going OD
Bill
