Hi Scotty I have a 2004 Chevy Silverado 1500 V8 4.8 231,536 miles on it and need your help with an issue on my truck. Every time I start up my truck for the first time in the morning, I put it in drive, press the gas pedal and I hear my truck gasping for air, kinda sounds like a vacuum machine. It stops eventually when I get to higher speed maybe 40 mph. This also happens when my truck is idling for maybe 10 min. I changed the spark plugs, added an cold air intake and did a muffler delete but I can’t seem to find the issue. It did the exact same thing with the stock air filter. I also scanned for codes and a P0420 popped up has something to do with the catalytic converter.
If it ain't broke, don't fix it!
Doc is right on this one
Adding a cold air intake and deleting the muffler have screwed up your truck and confused the computer.
It did the same thing even before I put on the cold air intake and took off the muffler.