Let try again,we pulled the motor out of my 15 touring. We pulled the head and found cylinders1+2 were running rich and 3-4 were very lean. Any help in locating the problem would greatly appreciated.
I would look at the intake manifold, suspect it is not sealing at the rear which would cause a lean burn in 3 and 4!!
I always put a little permatex around the seals when installing.