If your over / under, maybe Gearvendor, unit is working you should be getting progressive shifting through the gears when the unit is on. That means you'd get six gears. The unis give you in effect 1st, 1st over, 2nd, 2nd over.. and so on. This keeps you in the sweet spot for climbing but does not give you an underdrive on 1st gear with a GV.
1984 28' Funeral Coach
Former Rolling Showroom & PuttLab (now party bus)
"I'm not an expert. But I did sleep in an Airstream last night."