I've got a 2001 Z71 with the 5.3L and tonight I had to "punch it" from about 40 mph on a slight uphill and it started making a rapid ticking sound that I could feel thru the gas pedal. What gives? Was this pinging / knocking / detonation??? It went away as soon as I let off the gas. I only use 93 Octane from Exxon, Mobil, or Chevron. It has around 9K on it now. I've noticed since we bought the thing new that the 5.3L seems kinda of sluggish when you get on her. Any one else have this problem with the 5.3L? The noise from the engine really has me worried. One other time in the past, I got on the gas hard from a dead stop I got the rotten egg smell. Have yet to have a SES / check engine soon light. By the way, I only use Mobil 1 oil in it. Also, would it have been better to hit the tow/haul button before I got on it OR should I have dropped it down to 3rd gear myself OR both??? Really need some insight here.