There doesn't seem to be a solution. I looked at it again yesterday. I can unhook the cable at the door and the lever moves fine and I can engage the high speed fan no problem. Hook the cable up and the door hit's it's maximum allowed movement before I can move the lever far enough to engage high speed on the fan.
When I look at the cable, it still has room to go as it pulls the door, it's the door that stops, and it's fully open before the lever gets to high speed.
I tried installing a new switch mounted up behind the controls, hoping that the switching movements in the original might be a little worn and I might get lucky with a new switch. It did help to a degree, as I can push the switch further down about a 1/2" and hit high speed, but I let go and it moves back up to medium speed on it's own. When I watch the cable and the door while doing this, it's actually trying to pull the arm on the door further than it wants to go. So the cable isn't too long or too short, it still has room to go.
Unfortunately I see no adjustments anywhere, which seems odd to me.