I ran over an "alligator" on the freeway (truck tire retread) and had to replace all of them. First I had to figure out they are called deflectors. I thought it was some kind of sound proofing. Here are all the part numbers and links to help someone else.
The metal piece going across the front that is bent on mine is engine cradle brace 22957057. I ordered from GM Parts bin. It fit perfect and shipped quickly. The old one was rubbing against the exhaust and causing noise like it had a hole in it. I was surprised this part was only about $7
The part on the drivers side on the brace is 23363169 Front Compartment Splash. About $50
Passenger side REAR deflector: 23363172
Passenger side FRONT deflector: 23363171
DEFLECTOR, UNDERBODY REAR AIR REAR Drivers side 23363173
84052477 Large Drivers Side DEFLECTOR, UNDERBODY FRONT AIR( VEHS BUILT W/O MOUNTING HOLE NEED TO ORDER 23505514 TOGETHER WITH 11570498 & 11611806) $70 at gm parts giant.
If you lose the nuts you can get them too.
13280110 NUT, Front End/Bumper Filler NUT,UNDERBODY REAR AIR OUTER DEFLECTOR(13.5 THICK, FOR WELD STUD T5X14,2)(12.980)
11547637 NUT, Radiator Air NUT,FRONT COMPARTMENT AIR DEFLECTOR(NUT-HEXFLNGE,T5,20 OUTSIDE DIAMETER,10 SOCKET, PLASTIC) (1.269)