How many miles on your '04? A tight new engine will slow you down compared to a well-broken-in one. [ And I'm not sure where this 100# difference comes from - from the pontiac.com site the total weight difference between comparable 04/03 GTPs is only 24#.] Was the '01 GTP a coupe or a sedan? Was his gas tank empty and yours full? Was your trunk full of junk? These are all weight differences which can effect acceleration.

From a drag race simulator program, the speed difference between the two cars after a 1/4 mile race would be only 2 miles per hour - a pretty slow pull-ahead rate at around 90 mph. It would be much less at 45 mph. I don't know what difference the different final drive ratio would make.