My son's 05 Silverado 4.0L with 75,000 miles will almost not run. Start it up and take off down the road fine for about 2-3 minutes then the trouble starts. Idle is rough. Can press gas peddle to floor while sitting still and will never rev above 3,000 RPM. Small hill in driveway that takes 4WLow to get up. Driving on road and pulling hill slows to alost a crawl with massive misfires and very strong raw gas smell in cab as well as cars behind smelling. Took it to Advance Auto to check engine lights. Said it was 02 sensor. Took it to dealership who said it was bank 1 & 2 02 sensors, maf sensor, rotor & cap but CAT's were fine. Have replaced plugs, wires, maf sensor, rotor & cap but still no changes. Holding off of 02 sensor due to money. I think it's the CAT. When you drive the truck for a very short time the CAT's glow bright red. Driving behind the truck in cold weather and watching the exhaust, it never changes from idle to hard pull. The same amount of visible exhaust come out. Gas milegae is shot...it sucks the gas. Takes almost 1/4 tank to go about 15 miles. Also have a lot of noise in cab when pulling hill. Gets to the point you can't even hear the radio. Noise sound like it's coming back up around the breather. Can the 02 sensor cause all this or are the CAT's stopped up? If the CAT's are stopped up how do I get the dealership to fix them when they say nothing is wrong with them. I know the CAT's are still under warranty. At this point the truck is off the road and not driveable. Any ideas or suggestions? Thanks in advance for any help.