Sounds like a bad choke. I'd bet any other choke would make an improvement.
For your scope fog problem, I get some eyeglass defogger and use on it.
If the fog is happening on the inside of the lenses somewhere,
then the scope seals are band and it is time to go scope hunting.

As for the Mossburg 535, it is a great gun. The only thing I have had a problem with is the release just behind the trigger guard that allows you to cycle the gun. I have accidentally pushed it while taking a shot and the action come open a tiny bit and the gun won't shoot. The release is just in a bad spot.

Good luck.