2002 Mazda B2200 Oil residue on the spark plugs

My truck started vibrating, losing power going up hills and the check engine llight came on yesterday. So I went and had a Dianostic test ran to see what the error might be. The test came back with an error for TCS (throtle control sensor) so I changed it out and the old one was definately no good. The truck in park still had heavy vibations so I thought it maybe a ignition problem so I changed out the spark plugs and wires. When removing the old plugs I noticed that the plug had oil residue (not carbon) even a small drop of oil was on one of the plugs. After changing them out the truck still idels rough and has a huge decrese in power. Could this be head gaskets and rings? Mazda B2300 Thanx