Emm not sure on the 350 mate, but there are a few cars out there now that have learning ecu's. For the first x amount of miles the ecu measures the type of driving style I.e fast or economical....if you potter around you gain more mpg but slower acc and top end, if you have a heavy foot you gain the full bhp & ft/lb torque but lower mpg if you follow me..
Maybe you just remeber it been faster...lol..