2000 Ford F-150 help!

Hello I have 2000 ford f150 4.6 automatic 2wd I have owned this truck since it was new and have never had a problem untill now. It starts fine and when you are driving it bucks like its missing but there is no light on. It does not do it all the time just here and there. I live on dirt roads and drive it like its a baby but could it be a vacum leak and dirt getting into it. I washed the ingine down one day and it ran bad until the water dried up? And thats what it feels like its wet but is not. I put in on a computer and it could not find a problem. It has the plug wires with the coil built in and I have heard alot of people have problems with them. Fuel? Spark? I dont know please help you guys are great and I apreciate your help!