Navigator Runs rough 2003 model

Truck runs good up till about 55-60 then hesitates and takes a dump and runs s***ty. dealer says he needs to pull the valve covers. Chech valves 1,5,8 plus $600 WTf! I thought it may be fuel first; maybe inj or pump or filter anyone else got any great ideas?
It does pickup again at 65 mph and runs ok.
thanks,
Jim

Sorry I meant cyc258.
Maybe the coils any Ford guys got an idea the cide came up 89728