I don't anticipate any problems with grades on my '89 GMC based B. I don't know what gearing it has but it tends to lurch when I give it thottle. With a 6100 lb GVW I don't hot rod it but it's never lacked for power. The previous owner did some racing and I suspect it got "tweaked". The only problem I've seen on the road is high cross winds. It's a Coachmen Horizon and it quite tall. It's the first van I've seen with a second floor.
Unless you want to go fast up a hill, you can always shift your shifter to 2 instead of drive. That eeps it in a lower gear to take advantage of internal gearing and torque advantage from the converter.