One 3" exhaust has over twice the area as one 2" exhaust -- 3.14" square vs 7.07" square. I'd say your exhaust is too big. You could test it by partially covering the hole and see what it does to the temp.
Unless you're comfortable cooking there. Each drum will have it's own personality and if you're happy with it, smoke on.
The exhaust has a damper, so I will try closing it up a bit.
The pipes are my extended air intakes. I origanally had only one extended 3/4" and it seemed like I had air flow problems. I added the second and made it 1" and it seemed to work better. I am going to try closing the exhaust damper down a bit like Dave suggested.