As others have already said, my 1997 also has the vacuum reservoir under the wiper cowl on the passenger side... there's the check valve that feeds the line to the HVAC controls through the firewall with the AC lines (not sure about non-AC), then there is the second line left of this T-fitting that feeds up under the weather stripping and through to the reservoir.
Anyway, my problem was a bad check value off the manifold... I couldn't find a Mopar replacement part, and brand new Dormans failed out of the box.
GM/ACDelco part number 14047619 fit perfectly and solved my vent issues... and my cruise control is stable on hills now.