I looked at getting GV OD once. Number one, look at the COST!!!
Then math out the potential reduced fuel use incl. annual miles driven vs cost.
Unless you put on uber miles/year, it just doesn't work.
The other thing I don't like about add-on OD is, it's
another gearset in the drivetrain, which actually
reduces drivetrain efficiency as far as internal friction. The only reason it works at all is that the benefits of reduced engine rpms more than offset the increased friction disadvantage. To that I say, unless the vehicle is so heavily loaded that it needs 8+ forwards gears, one is better off getting their top cruise gear lowered via regular transmission or lower rear end ratio or both.