I can't comment on gains with JUST a stall but I did LTs, exhause and the budget Circle D 3200 and went from 14.50 to 13.82 with me behind the wheel. The truck went 14.30 before those mods with my cousin behind the wheel (I'm fat...he's not). The air was great on the 14.50 and not so great the day of the 13.82.
2005 Silverado SS AWD
AEM CAI, ARH LTs, HD-2 shift kit with vette servo, Circle D 278mm 3200 stall Madtunesracing.com street tune (MTR now has a Dynojet 248 chassis dyno)
13.82 @ 94.92 w/1.83 60'