oil in the intake

okay. I need some help. I have a '96 3500 with a 350 vortec. I just dropped a remanufactrued motor in it but I'm having some problems. It has started running a little rough. And not just at idle, but throughout the rpm range. And it's a little slugish. I tok it to a mechanic after not being able to figure it out myself and they said they pulled the #8 spark plug and it look a little fowled. I have great compression so they think it is the fuel nozzle. However I took the intake cover off to look at the injectors and found that some oil had settled around the #8 intake port. What could this mean and could it be why it is running rough. Thanks for your help.