I got the truck back and I have some test results. They conflict a little with what I was told over the phone. I'll comment after the resuls.

The first number is at 15mph (~1850rpm) and the second is at 25mph (~2047rpm) on the dyno. I also typed out the reported average emissions for passing vehicles.

Test 1 :270 cam, old cat
HC(PPM): 206/225 avg43/32
CO(%): .63/.62 avg.16/.15
NO(PPM): 719/725 avg406/349

Test 2: stock cam, old cat
HC(PPM): 198/181 avg43/32
CO(%): .64/.60 avg.16/.15
NO(PPM): 934/815 avg406/349

Test 3: stock cam, new cat
HC(PPM): 35/18 avg43/32
CO(%): .03/.01 avg.16/.15
NO(PPM): 25/16 avg406/349

From test 1 to test 2, it looks like swapping to the stock cam slightly decreased HC levels. The NOx levels, however, increased. Am I correct that by reducing HCs (unburnt fuel), the exhaust temps probably went up slightly, which caused the increase in NOx? Am I also correct in saying that the changes between test 1 and 2 are subtle and the 270 cam does not significantly affect emissions?

From test 2 to test 3, you can see the new cat cured the tailpipe emissions. I don't even know if I can believe the last numbers they cranked out with the new cat. Is a catalytic converter really that much of a miracle worker?

Based on how broken up the old cat was, I imagine test 2 reasonably represents the exhaust upstream of the catalytic converter. Does this seam high for out-of-the-engine emissions or is this normal for precat exhaust emissions?

I don't want to melt down another cat so please let me know if you think I should persist in finding the real problem.