P0263 coode

Question

I have a 2004 F350 6.0 with only 36500 miles. When driving it will sometimes surge or accelerate on its own then shortly after will start missing at idle. this has happened several times anf not set a code or turned on check engin light. I had the head studs and gaskets replaced and EGR deleat along with a sct programer. the problem went away for a couple weeks then started again. It finally got bad enough to set a P0263 code and now seams to run rough more then not. Planning a long trip with the camper this summer so any help would be great.