Hello Bruce.
I know how frustrating it is to build something with such high expectations and not have it work like you want. Been there, done that, and been there again. Now is the time you must be tenacious.
The photo below is of my first attempt at an aerodynamic lid, the white truck. I too used an existing camper shell I had built some years earier as a starting point. As you can see, the slope of the white truck cap is too abrupt. The silver truck in the foreground is the clay model I was sculpting for the lid I have now. That slight difference in angle makes all the difference in the world.
CarloSW2 and others are correct in illustrating the slope of your lid being too abrupt. My first lid had to same problem and did'nt improve the fuel efficiency of the truck at all! Aerohead explains it best as the air separating from the surface of your lid and becoming turbulent. I hate it when that happens. With a correction in the angle of your lid and development of the back surface as NeilBlanchard and skyl4rk suggest would make a great difference.
On my lid, I got lucky. I sculpted the angle of my lid to what looked like it might work and again, it was dog luck I got it right. I consider myself honored to be in the company of many here on ecomodder that posess knowledge I would love to have. I have learned a great deal about aerodynamics from many here. I can do one thing though, I can make shapes and quickly too.
Bruce, give me a shout at
aerolid@aol.com. I may be able to help you on making the modifications to your lid. In one weekend we could knock it out if you would'nt mind driving to Little Rock. I know you are in school, but maybe we can work at a time to get it done.
Bondo