HEADS UP !! Extruder carriage not level...
I've been going crazy trying to level the nozzles on my dual extruders so I decided to level everything that I could possibly check on my printer. I found that my extruder carriage was not level but the travel rods were. It turned out that one of the bearings was not "seated" all the way into the plastic carriage, someone at the factory goofed. Using a pair of slip joint pliers I very carefully squeezed the bearing into place now everything is level....So if your having this problem ...check those bearings!
You can buy a small 3 inch "line level" at most big box or hardware stores, it works great.
Don