I am looking at what is listed as a 2003 Coachmen 258 DB with a Chevy Chassis. I think it probably should be a 285 DB ? It is advertised as having the 5.7 engine which seems a little small/underpowered for this size of a unit ? I had an 02 Chevy van ( 1500) with the 5.7 and it towed OK but it just seems a tad undersized for this unit . Does this sound right ? Any ideas of gas milaege ? Thanks for any assistance.