[brucepick]

All comments I have to say are true.
Especially the note that a tire pressure increase across the board would save large quantities of fuel. I'd like to see all cars with 51 psi tires and a placard spec of 45 psi or so. Mid-30's psi is so old school, imho.

HOWEVER
I don't see a big issue in what GM recommends as a fix for the missing welds.
Missing welds to be substituted with rivets and/or nuts and bolts.
Um, did any of us ever use fasteners where a weld might be better???

I wouldn't expect that remedy to remove or otherwise disable the aero benefits of the shield. Maybe a bit of extra drag from a screw head. But then, my car's aero belly pan is full of screw and rivet heads, and worse.

I'd say that an increase in tire pressure would more than compensate for any minor increase in drag due to the use of fasteners.