2001 chevy hd 6.0 mis on 1 3 4 rough idl - 2001 Chevrolet Silverado 2500HD

SOURCE: strong gas smell and idles rough. did tune up. no

look at the fuel lines and injectors for signs of leakage.

SOURCE: 97 chevy pu 305 vortec, had cyl 6 misfire and

thats usually a sign of a vacuum leak, recheck and make sure you don't have any loose hoses, or cut intake seals

SOURCE: 2006 Chevy Trailblazer is mis fire on cylinder 1

Not without seeing it, but...
Coil pack are common on those. If you have the in-line 6 cylinder, it would be the front cylinder. While idling, unplug the harness for the coil pack on #1, if you have no change in the way it runs, your problem is in that cylinder. Try another to see the difference, as it should stall. I have "swapped" them around to verify the issue.

SOURCE: Why would a 2001 chevy blazer idle rough?

Could be a few things. First off, are you getting a Service Engine Soon light? If so I would get the read out code from that to help narrow down your problem. You can always head to an auto parts store and usually they will let you borrow a OBD II code reader for free.

If you have not already. Check your air filter and Mass air Flow sensor. Make sure its not plugged up and causing the MAF to cause problems.
Best of luck!