Why is my 1999 ford f250 acts like it wants to do? on 1999 Ford F-250 Super Duty

When you start it up it runs fin for a min then it acts like its missing and going down the road it esatats for a second but when you punh it it takes right off. It has the 5.4v8.the kid that owned it be for me said he put all new coil packs and no engine lights are on.