I had the exact same problem and it drove me nuts trying different fans, moving the radiator and adjusting the shroud. When I put in the new engine, I adjusted the motor mounts and the transmission mount about 1/8" to center the fan in the shroud. There is a small amount of play in those bolts (the mounts that bolt to frame) which allow a little adjustment. Now the fan sits in the shroud as it should and even gap all around.