ok trying to help my father with his truck he bought with a bad engine has a 5.4l in it he had a 2000 5.4 two valve with 45,000 on it in garage. so he proceeded to use that by putting the 2009 heads and intake on it put new timing chains and phasers and oil pump in it. we put it in and it runs good sound great until its put in gear and rpms drop to 450 and then it start clattering like a Diesel and runs rough as hell. once rpms are picked up for a minute it clears and runs good. I am trying to help him he bought this the first of September hoping to take the fifth wheel and my mom to Florida for the winter a few days later mom was told she had leukemia and she passed on the 16th one of the last things she said was she wanted to get to ride in it before she died so it means a lot to him now.

 

just found out he used 10w-40 could the oil be the problem?