Hi Matt,
Well, based on the data you recorded, here's part of what might be going on:
P0455 Evap large leak. Could be a gas cap issue - make sure it's on tight and there is no rust around the cap seal. We have also seen fuel filler necks get rusty and cause this. Could also be a stuck open evap vent valve - seen lots of these on GM's. If this is venting when it should be closed, it will trigger code now. Your scan tool might give you Evap Vent Solenoid parameters - look at these.
P0171 & P0174 - could be leaking intake gskt, cracked air snorkel between MAF sensor and Throttle body. I have seen this personally! Computer relies on MAF for how much air engine is getting. If you introduce "extra" air, it's unaccounted for and will set code. Because it's on both banks, look to see what would affect both banks.
Fuel Trims running rich
Coolant temp 82* C means 179*F - OK
Intake Air Temp - IAT show 62*F means 143*F - This is a problem.
This show me the computer thinks the air coming in from the outside is 143*F. I don't think so. If the IAT is part of the MAF, this might be a failed component. Disconnect the MAF sensor and see if the IAT number changes.
I'm hope this helps partly - If you have more questions, call me at 1-231-203-3072.
Scott Castleberg
Pellston, MI
Gadgetman Michigan