Thanks to those who responded to my earlier post regarding the problems I'm having with my 6.5. I have finally gotten around to removing the upper intake manifold and cleaning it out as suggested. I've had the PCM reset (it displayed p0401 & p0406). One day later the check engine light is back on.

The other things I've tried prior to this include replacing the vacuum pump, both egr solenoids, the waste gate solenoid. the MAP sensor and I've had the wiring harness checked for shorts.

The check engine light will come on at highway speeds with no noticable change in performance. Twice in the last week when accelerating away from a light I've experienced a lack of power and noticed great clouds of black smoke spewing from the exhaust. It lasts for 3 seconds or so and things are back to normal.

The mechanic wants to replace the computer but admits he has no solid evidence that this will solve the problem.

WHERE THE *#&& DO I GO FROM HERE!!! Any and all thoughts are appreciated.
thanks
alex

PS While I had the upper intake off I got out the die grinder and removed some material from the upper plenum. Seems to have made a positive difference.

How about the firewall baro/egr feedback sensor, also check for leaks in the EGR diphragm, what kind of vac are you measuring from vac pump, and across solenoids

when you had the upper plenum off did you replace the metal doughnut gasket that sits in the center of the lower plenum that seals the egr feed? kennedy's site under tech tips has pics, he calls it the "mystery gasket". if you got the info on the grinding from his site you probably did replace it but it is something else to check.