Thanks for the response.
I haven't looked into Nexus because when I asked at the border what the benefits were versus cost no one could really give me an answer. The only thing that I was told was that it would let customs know that cross the border frequently. I'll have to go out on the net to see exactly if there would be any benefit for me. I think since I've never had problems in the past crossing through the tunnel that I never gave it much thought.
I'm wondering if the fact that I usually cross at the tunnel versus the bridge was something that "flagged" me. When crossing at the tunnel I usually see several of the same customs agents and perhaps they know from my record that I cross frequently. Actually, the only times I've been stopped have been when crossing at the tunnel so I think they do pull people over even if they're familiar with the people crossing.
I'm not sure if I consider myself lucky or not that I haven't been pulled over more often. The Detroit/Windsor border has a lot of traffic going back and forth daily and I can't see them targeting people that cross on a regular basis. I do expect to get randomly pulled over every so often but it was the fact that I was marked as a "Previous Port Runner" that actually bothered me.