Nice looking build, it's kind of an offset-UDS. First step is definetly a couple new thermometers to find out whats going on in the cook chamber.
I'm thinking you might also have an air flow problem thats limiting your fire. Four 3/4 inch inlets only gives you about 4.7 square inches inlet and the 2 inch outlet only gives you about 3.1 square inches out. My gut says thats too small for an offset but there are lots of UDS builds with about the same; difference is the fire is in the UDS, not offset. I've never used one but maybe one of those BBQ Guru things with a blower would let you improve air flow without cutting more or larger inlets and exhaust. Let us know how it turns out.
PS: did you say you keep the exhaust closed when cooking? I would think you need at least the 2" open to get proper draft & larger might work better.
Weber 26.75 OTG w/CI grates & SJ/WSM Mini
Home built 24"x72" reverse flow stick burner trailer with 18"x44" grill w/CI grates and upright SS gas oven/smoker.
Home built 48" fire pit with a 30"x30" Santa Maria style ranch grill.
Home built lump charcoal retort, iGrill & a bunch of other cooking toys.
Last edited by dwfisk; 03-28-2013 at 02:56 PM..
Reason: Added postscript & clarification