I had a 1999 wagon with the Vulcan. Pennzoil 5w30 conventional did the best as far as engine smoothness, MPG and used oil analysis. I used/tried Mobil 1, Chevron, QS and Mobil drive clean in that engine.
Its got 160k on it now and needs a new transmission. Also needed 2 sets of head gaskets (61k and 108k).
Bill