Well Mark, I may be a little late chiming in here, but I just happen to be resealing the intake on my grandfather-in-law's '99 suburban. I snapped some pics of the bare intake to illustrate what I believe may possibly be the issue. The particular truck that I'm working on is a 1999 Chevy C2500 Suburban with an L31 5.7 (obviously) and a 4L80E. Mechanically, the '96-'02 L30 and L31 intakes are essentially identical AFAIK. Anyway, I've got a couple things to do and then I'll upload my pics to the computer and post them with a few notes showing the passages and such.