8.1L EGR Codes & Stalls When Putting In Gear

[ltrmc02]

I have a 2001 GMC C6500 with the 8.1L that after it warms up will not stay running when shifting into gear, Allison automatic.  If I shift it into gear and quickly give it throttle it'll take off and run fine and I can bring it to a stop in gear if I do it very slowly but bringing it to a stop normally it'll stall out.

 

I'm getting P0404 and P1404 codes, both EGR related.  I cleaned the EGR and checked the solenoid and it'll open and close fine.  I put a block off plate under the EGR to see if it would act different but no change and I've since taken the block off plate back out.

 

I was suspecting a vacuum leak or IAC valve issue but can't locate an IAC valve and the only vacuum hose I see on this truck is going to the fuel regulator and that line is good.  The brake system doesn't use a vacuum booster on this truck.

 

I also have a 2001 2500 Suburban with the 8.1L also and so far I've swapped the throttle bodies between the two engines and no changes.

 

I found one forum thread mentioning the EGR passage gets clogged and to clean it the intake manifold has to be removed but I can't find any information on this procedure.

 

Anyone think EGR flow restriction could be causing my issue?