Make sure the harness connector is making flat contact with the ecu, sometimes if the bolt is tightened to much the outside edge stick out.
When you say the boost gets stuck at 10 then jumps to 15, do you actually feel the extra boost come on? if you don't feel it act the way it shows then it may very well be the gauge itself.
Also I would check the readouts on the MAF, how are the o2 sensors?