Littletunny,
I don't think Bushwhacker was actually recommending vertical scuppers.
Vertical scuppers are only good underway.
I would suggest you take a closer look at your problem. First determine why they drain slow. Diameter of drain tubing? Is tubing flange elevated causing water to exit uphill? What is height of floor in relation to waterline? Where do transom scuppers drain in relation to floor and waterline, etc...
Assuming the angle of egress is favorable, I would consider changing the size of the tubing and fittings and putting ping pong ball scuppers on the transom to keep water from coming in from the aft end. If the drains prove to be running uphill, change that angle. A factory error in that regard is very possible...