My check engine light came on yesterday and started blinking. I ran it to pep boys to get it scanned. It came back to P0300 multiple cylinder misfire. My truck is a 2000 Chevy Silverado 1500 with the 5.3. It has 182k miles. I replaced fuel pressure regulator and spark plugs. Neither ended up working. The truck smells like gas when it idles, and feels sluggish when you drive it. It seems like it drives fine at times then it starts to shake. I cant seem to figure this out. Any help???

**Edit with more information**
For the past 6 months or so, the truck would take an extra second to start. It would crank for a second, and I would give it some gas and it starts right up.

To go into further detail about the truck, when the check engine light came on it started to drive different. It was backfiring really bad in the morning. When I drove it later in the day, it seemed like it back fired less. It feels sluggish when you accelerate, or get on the gas at all.

I am far from a mechanic, but I am rather handy. I would like to fix this on my own to save money. I understand that going to a mechanic would be the easiest thing to do, but I cant really afford it at the moment.

 

Been a few years I see, but I am having a similar problem. What ended up being the cause?