I have a 1999 gmc 3500 crew dually with a 454 engine in it. This week it started running rough and idling funnny. Could this be the fuel filter or something else?

Check the oil first, the low oil sensor will disable the ignition if more than a quart low. Miles on this truck warrant a new fuel pump and fuel filter. GM fuel pumps, don't handle Methenol Fuel very well.(water).

What engine ? 4.3 , 4.8 , 5.3 or 6.0 l What fuel injection system ? What is the fuel pressure ? Do you know what fuel trims are ? The fuel pressure regulator's are prone to leaking to leaking on thses SPI injection system./
How to identify and repair leaking fuel pressure regulator GM CPI system...

Hi,
Did it run correctly after the rebuild? If so, has it gradually gotten worse or just all of sudden started having issues?
If your fuel filter was plugged did it run better after changing it then get worse? If so, you may have rust in your gas tank. Has the truck sat w/low fuel thru a winter or 2?


I'd consider getting the fuel injectors cleaned - meaning removed - not just the 'service', or just get new/lower mileage ones. I bet they're avl. on the Chevy forums for a lot less than from the dealer.


If you have over 100K miles on the rest of the truck, sensors may need replaced.
Things to check:
1. MAF (don't know your engine, may be irrelevant)
2. Oxygen - O2- sensor - may have more than one
3. TPS - throttle position
4. Idle control - (don't know your engine, may be irrelevant)
5. Fuel pump
6. Fuel pressure regulator (don't know your engine, may be irrelevant)


I'd go check on the Chevy forums for more info...very likely your exact issue has occurred before and been fixed.


GL,
Td

Assuming the check engine light is not on, I would check for vac leaks and the fuel pressure at the injectors.
That vac leak could involve the EGR valve among other things.

spark plug wires or coil pack

Sounds like you might have a bad fuel pressure regulator.You can check it by pulling the vacuum hose off it and if you see any fuel run out then the regulator is faulty.

You need to look for a hole or loose fitting clamps where your air duct runs from your air filter to the throttle body where the gas enters the motor. Any leak in this ductwork will make your vehicle hard to start and run poorly because too much air is getting past the mass air flow sensor.

ROUGH IDLING CAN BE CAUSE BY MANY THINGS.I AM LOOKING AT LEAKING VACUUM HOSES OR INTAKE MANIFOLD GASKET LEAK.DIRTY FUEL INJECTORS AND WORN ENGINE VALVES WILL CAUSE ROUGH IDLING.ALSO LOW IDLE SPEED CAUSE ENGINE TO RUN ROUGH.

It may just need a good tuned up?

sounds like fuel pump