1991 GMC Sierra Engine runs rough

When engine is first started it idles fine. When accelerator is engaged the engine spurts and sputters as if it is getting too much or not enough fuel. When the engine is warm it runs smoother but there is always a hesitation when the gas pedal is first depressed. Other issues that may be related include a significant amount of carbon from the tail pipe when the truck is at an idle and dirty oil immediately after an oil change.