We have a 1996 RT 190P on the 3500 chassis. All the 1 ton vans came with the 3.93 rear axle. My older late 80's B2500 had approx. 3.5 axle ratio. This could make the B3500 as responsive as the B2500. (provides more torque to the ground, which is what gets you up the hills.) You might want to check what the axle ratio is on you RT 170 to compare.
My 190P has preformed quite well 15 - 17 MPG and acceptable torque for the hills. I live in the mountains. It weighs 7640 - 7880 lbs depending on load. I don't think the PW will be much heavier but I know it is a little.
Our friends have a 2000 year PW and don't have any problems. I would pick the one that works best for you.
Good luck