David, what are you thinking the possibilities are? 1) the catalyst, 2) the egr? Or are you thinking of something else.

I'm going to check the EGR tube soon to see what's up there - if it's clogged then there's at least a contributor to the problem.

If I understand the process, the EGR contributes little to the emissions system at or just above idle, so if the tube is clogged/restricted, the impact would be most noticeable in the low-speed test, which is where I came close to failing.

Curiously, while watching the test, I saw something I don't remember seeing before. After the low-speed test @ 15 mph, there was period of time (about 90 seconds) where the computer requested a speed between 15 and 25 (I don't remember what it was) - then the computer requested the 25 mph run.

Maybe this is always the way the test runs, but I don't remember it being like that before.