This morning I got up and tried starting my car and it started up very rough then the check engine light came on. I took it down to shucks and they pulled the code P0300 "Random/Multiple Cylinder Misfire Detected". I'm lost on what it could be this last summer my fuel pump went out and I replaced that and the fuel filter and it's been running fine. Last night it ran perfect no problems at all when I ran to the store. But now this morning its idles rough there is a black dust coming from the exhaust. When you accelerate it starts off rough the RPM go all the way to 4,000 to 5,000 before it shifts. Its going through gas like crazy I had a half a tank this morning drove about 5 miles and now it's almost to a quarter. Can someone give me some suggestions before I take this thing to the shop? One other thing I noticed a few days ago that my Trip OD said 436 on it I'm pretty sure just a couple days before it said something like 38 since I reset it every time I fill up and I had just filled up over the weekend. Could this mean a computer problem?

Thanks