So within the last couple months my 98 Silverado 2500 (350 Vortec) started having an intermittent issue after driving it throughout the day. It will startup and run fine first thing in the morning but the more I drive it during the day the worse it runs. The RPMs will start bouncing up and down and it will act like it isn't getting enough fuel. The only code it has thrown was codes for O2 sensors (which I replaced last year). I also just replaced the exhaust flange gaskets and that didn't make a difference. I have also replaced the fuel filter and spider harness. Testing the alternator from a cold start I was getting 14.6 volts. The truck has right under 289,000 miles on it so I'm trying to figure out what could be causing this kind of issue without it being consistent. I haven't had any codes come up in over a year until just the other day and once I replaced the exhaust gaskets and cleared the code it hasn't come back. Thanks in advance for any ideas.