@Keith Seymore - There's a wealth of info in those docs you linked to. Thank you again!
For posterity, looks like my tow capacity is 7,000Lbs, with 3.73 gears. 4.10 would give 7,500.
Interestingly, the R2500 w/4.10 & tow package can tow 9,500! I'm kinda surprised 4x4 decreases capacity that...