Every once in a while, I wonder if the ECU is pulling timing, causing that effect. I imagine it might be the sensitive measurement sensors, like the air temp, MAP, or MAF that are sending readings to the ECU, and the ECU is adjusting. Air temps can change quickly here in Vegas, especially when you drive by a pond or other small body of water. This probably confuses the ECU sometimes.
Kinda like those stories about Evos stalling out when someone with an obscenely loud exhaust would rev up at them?