i like the way the 2005-9 mustang fastbacks look.im tired of dealing with convertibles.i want to buy a 5 speed mustang fastback,black interior.[never sand colored]i thought i should be looking for a 4.6 since its mph is only one mpg less than the 4.0.which are more reliable,4.0 or 4.6?which is the better engine?btw i have a small travel trailer i hope to haul.