The only thing I can think of, and prolly what others will tell you is that it is probably moosing...but then again it is happening while you are accelerating, usually moosing happens durring idle, so I dunno.
check under mods for "Throttle Hang fix"

SVTcoop

98 Black CSVT Indiglo Gauges, including HVAC, KKM Intake Exhaust: Brullen loud system with 4" tips, Moddified stock Y-pipe Sound System: Alpine 9815 Deck, Alpine SPX-177A comps, 2 Lambda 12" subs.