We chased a random multiple misfire at one point and the culprit ended up being a new-ish cap. It was crossfiring in the cap itself. They're cheap enough that it might be worth trying that. This is where it would be nice to be able to check the plug wires to make sure they're actually firing...
If the arm is hitting at full droop (when the tire was off) that's fine, it's a droop stop. The key is to have some down travel left in the suspension when it's at ride height. The arm does not move very much that close to the pivot point so a little space there goes a long way. The thing to...