TREMEC has a slick formula for rpm:
rpm=(mphxgear ratiox336)/tire diameter in inches

Your AOD has a final 0.67 ratio. If we assume a 30" tire diameter, want 2000rpm at 70mph cruise and solve for the Gear Ratio,2000 = 70mph cruise x 0.67GRx336)/30 you would need a 3.8 ratio. A 3.73 is close, so lets run that, and you get 1959rpm at a 70mph cruise - about perfect, IMO. You need to plug in your actual tire diameter - Tire Rack does not list a 275/75Rx15 as being an available size.