random cylinder misfire

[2000 z71]

I have a 2000 Silverado with a 5.3 vortec and over 200,000 miles on it.
It started having trouble starting about a year ago. It crank a few times before starting. Over the past year it increasingly got worse to the point now where it takes a long time of cranking to start. Once it is running it runs very rough almost to the point of stalling. but once you are moving, and going down the road there seems to be little or no problem. It starts best if it has been sitting for say overnight. I took it to an auto parts store in town, and the code they came up with was a random cylinder misfire. I changed the plugs, no help. I changed the fuel filter, no help. I changed the plug wires, no help. I have removed the coil packs individually, and no noticeable difference.
I have heard that the problem maybe related to the catalayic converter. I don't have clue what to do next. Could someone please help me to find a fix the problem.
Thanks Bobby

[tom3]

If it still has the original fuel pump, that's where I'd start. Might try a new fuel filter and see if it helps a bit, but this sure sounds like a pump going bad.

[maxwedge]

Bobby, good chance a professional could fix this for you by doing basic fuel system tests, rather than guess work parts replacement.

[GMMerlin]

Maxwedge is correct, throwing parts at your vehicle is not going to be a cost effective way to repair your vehicle (although it seems to be the norm around here)
I laugh at the people who spend hundreds of dollars to throw parts at the problem instead of spending 80-100 dollars for a professional diagnosis…but hey it’s your money
A random misfire code just tells you there is a misfire, it doesn’t tell you what cylinder or cylinders are misfiring.
First thing is to determine which cylinders are misfiring, then determining what is missing from the AIR,FUEL,SPARK,COMPRESSION equation to cause the misfire.
Proper diagnosis is the key.
A catalytic converter can cause a misfire, but a lack of power on acceleration would also be felt.
Personally, (after some basic quick checks) I would start with the fuel system on this truck and work from there.
Fuel pressure and injector balance will determine the condition of the fuel system and a quick visual inspection of the fuel in the rail will tell you a lot.
No need to replace a fuel pump if it is good and holds pressure (I have many customers with 3-400K miles on their vehicles with the original pump still in them).
Simple things like a dirty throttle body can cause a hard start and rough idle concern, what about a leaking FPR?

[2000 z71]

Thank you all for your input. You all make valid points about not throwing parts at the problem and just take it in! I had given thqat some thought considering I allready have put $200 into the problem with no results.

I will let you all know what I find out.

Thanks again,
Bobby