1987 3.5 efi crazy missfire

[ozzytupo]

Hey I just got a Rangey with 108000 miles. I've been having a puzzling misfire which causing lumpy idle and lack of power thorugh the rev range, sounds more like a 5 cylinder car. I changed rotor arm, distributor cap and leads. Ran tonight and it ran incredible, all the power was back and smooth, even up to normal operating temp. Parked up at shops, came back 3 mins later started her up and started running **** again. It does have high lift cams and had a recent new ecu + I got the old one too. What could it be? Should I change the spark plugs?The misfire is consistant not intermittent, checked oil and water and no sign of head gasket. I thought it may be fueling but when it starts doing the misfire you can smell the exhaust is richer with fuel. I popped the plugs out today and they looked fine. Its just annoying it was running perfect for 30 mins, park up and it runs *****. Any ideas I would be grateful!!!