egr or head gaskets?
 

As some of you know, I'm on the verge of a tear down on my 06 6.0. I want to do some digging to see the actual problem before I do. Symptoms I had was while towing a trailer. Truck over boosted to 40 psi, all stock, for about 20 seconds. Then came white smoke from the stacks and puking out the degas bottle. Truck idles great and has great power and no more smoke or puking. I replaced the cap with a new stant one to see if that was my problem.

With that being said, I know the turbo needs pulled and gone through. What other tests can I do to see whether it is the HGS or egr cooler causing my problems?

Hook a gauge to the radiator line into degas bottle and check the pressure while running. It should stay around ~10psi normally, but shouldn't go over 16psi.

There's a vacuum test for the EGR cooler while installed in this TSB:
http://www.phila.gov/fleet/Warranty%...sb09-08-03.pdf