I have a 01 Chevy 2500 HD its been sitting for 2 years so i pulled it out of the weeds and done a few things and i need a little help trying to diagnose a problem.

its throwing a random misfire P0300 i believe,,,,,, with a service engine soon light FLASHING.


replaced..
transmission
oil
oil filter
fuel filter
air filter
plugs
wires
coil packs
cleaned the mass air flow sensor
also ran sea foam and 2 tanks of fuel through it

however i have a "service engine soon" light that only goes off SOMETIMES!! when cruising about 50-55mph OR!!! slowing down to a light or stop sign.

Any advice will be greatly appriciated and followed up on.

 

I'd suggest go back through check everything, i.e. plug wires on tight. You have a general misfire according to your post, might be worth pulling the fuel tank, and possibbly replacing the fuel pump. At least check for anything that could be obstructing the pump

 

thanks yeah i figured that would be my next step.