hi i bought a 1987 ford f250 2wd single cab truck a few years back had 95k on it now has 130k on it all original had glow plug problems and alternator problems and the dash cluster is kinda wonky fuel temp and oil pressure works then it don't. not a big deal but now we have a problem with it it runs great then all of a sudden could be days or minutes later missing but if there's a trailer hooked to it runs like new yesterday we pulled a 855 john Deere with it no problems un hooked the trailer it started to miss. but at a idle and smokes blue also when it runs bad going down the road but not all the time any help will be appreciated.