hello, well my truck started acting up the other day, its a 2003 silverado 2500hd 8.1L, allison trans, crew cab. what its doing is... on the highway when i step on the gas to pass someone there is no power. it almost sounds like its not running on all cyl. if i hold the pedal to the floor after about 3 seconds the check engine light starts to flash with p0300 coming up (engine misfire detected)that is the only code that comes up, and thats the only time it will come up. if i push the pedal down when its acting up and release it before th light comes on i get no other code. even if i push the pedal lightly the truck almost starts to buck a little like it wants to die. but driving around town or on the highway with out any load its fine. ive got a new air filter and a new mass airflow sensor. but i have no idea whats going on. also in the morning before the truck gets up to temp and i hit the gas hard the tires nearly break loose and there is plenty of power. it starts to happen when the truck gets hot. can someone please point me in a direction thankyou. - - - Updated - - - Not one person can help at all?