Pinging is caused by too much timing rather than not enough fuel (within reason of course). The 01-02 f-bodies have a tendency to ping just on motor, add nitrous to that mix and it's going to ping. Punch out the screen of the stock MAF ends, make sure the MAF is nice and clean with some electronic component cleaner, and email me to setup a tune. It needs to be tuned properly for the bigger hits or it will remove a piece of your piston or worse.

**edit** Just read that you had 109 in there. Was it straight 109 or just a few gallons to your 91? You shouldn't be pinging with 109 in the tank and stock timing.