I have a 1999 f250 6.8 V10. I purchased the vehicle with a motor having been installed at the dealership 10000 miles ago.It has a 36000 mi warranty. It started missing the other day so I took it in and they told me to start at the #5 Coil and plug. Did that. Still running rough. It has good power when you gun it and then when you let off and just give it a little gas it shakes badly.It will only get to about 60 on the speedo and sounds really bad. Should I just keep replacing coils and plugs until I get lucky.Dont want to really let dealership do that and they charge 100 every time just to tell me what may be wrong with it.