My 2005 Mazda 6 is cutting off with me and it is skipping really bad.

What is your question?

It shows multiple misfires but I have had new plugs put in, a new battery and the coil packs checked. My check engine light comes on and off. The dash lights get dim for a second with the check engine light flashes on. It cuts off mostly when I slow and stop. It seems not to be getting enough gas to keep it going. Sometimes before it cuts off I can only go up to a certain speed (40mph). Someone gave me the diagnostic codes p2229,p0300 & p0421 and told me that is what is was showing. Please help me....Thanks