I think I would try moving the tanks left to right, and see if it is a problem with the change over switch. Open the new "Drivers" side valve first, and it should switch to it. Then open the passenger side (that used to be drivers side) and make sure the tank is feeding properly.
You might have a problem with the tank's excess flow switch, or something else. Modern tanks have a flow limiting device, that should stop flow if the flexible hose breaks, or at least slow it down. THis device should stop (actually slow to a trickly) the flow if it is going more than about 150,000 Btu's per hour. By closing the valve, then open it again slowly, you might re-set the device.
Good luck,
Fred.