aight so my brother owns a 99 F-150 with the 4.2 v-6. has about 160,000 miles on it. we had to replace the engine at 100,000 (metal shavings in the oil FTW:thumbsup so we got an engine with 50,000 miles and had a shop swap the two. after a year or two, the engine started misfiring. so we changed the plugs, and the wires, which fixed the problem for about a month. when it developed the misfire again, we took it to a shop, where they said they didnt see anything. it misfires in 4th and 5th gear when you try to accelerate. y'all got any ideas? my brother loves his truck, but i seriously think he needs to find a new one.