You'd be better off with a trike from the experts, like ICE, Catrike, or TerraTrike. Your problem is the very high center of gravity -- it's built in, no amount of playing with air-pressure or suspension will change it.
Visibility is NOT a problem with the lower trikes, don't let anybody fool you. I've ridden 7,000 miles on mine, I can think of only one close call, and that's because I wasn't paying attention.