Pull the vacuum hose off the fuel pressure regulator and smell for gasoline in the hose. If you smell gas, replace the FPR. If the FPR seems okay, you definitely need to check fuel pressure. Autozone will rent you one (I think you get your full deposit back when you return the gage, so it ends up being free). If you want to buy a fuel pressure gage, Harbor Freight will have inexpensive ones. You should also have Autozone scan your car for diagnostic trouble codes (for free) as that will help to understand what is going on. You probably have a P0300 code, which is a random misfire, but a scan will help us to see if anything else is going on.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)