GMC Repair: 2002 gmc g350 van, dielectric grease, p0300

Question
i have a  two codes p0300 and p0351   have  a mulity misfiring  but   it  dont say  witch  one's

Answer
I had the same codes come up on my 1999 Dodge Ram. When you get a code, it will not say exactly. However, it will get you very close to the exact problem. When I had mine, I check all the plug wires at the plugs and the distributor. In your case you may have coil packs. Pull the wires, ensure there is no corrosion on either end. Go to the auto store and get some dielectric grease and apply to each end of the wires. Recheck the vehicle for codes. If you have a distributor, pull the cap and check for carbon build up. If need be, replace it. I personally recommend you replace it with a MSD cap and rotor. Let me know the result.