904 with overdrive???

Check your rear gear ratio,because the O.D will only benefit you if you have steep gears like 3:73 or higher numerically. 67dart is right,the motor will lug if it's out of it's powerband. Also if you have an A500 with locking tq,it may not lock up depending how much converter you have. But you did say stockie right,so this should not be a worry