check all your electrical connections to your pumps. in particularly to the high pressure in-line pump on your frame rail. ive got an 86 ranger 2.9 and its given all the same issues to me. hint to you tho.. check and re-lube all rotted electrical connections, these trucks are an electrical nightmare. i did so one day, lights were brighter, radio was louder, and once i properly took care of my pumps, my engine ran better