I am looking into buying either a 2010 Ford F-350 Lariat DRW with the 6.4 engine or a 2012 Ford F-350 King Ranch DRW with the 6.7 engine.Both trucks have about 20,000 miles.I can get the 2010 for about $38-39,000 & the 2012 for about $46,000. My ques...