HELP
 

I have a 97 F 250 powerstroke.
My truck loses power goes to like 10 mph then gradually gains power again gets to 55 or 60 and does it again. Hard tokeep running when cold. runs real ruff then smooths out again. We have changed the fuel filter, air filter, Fuel pump made some difference, Just changed the cam position sensor. No luck any ideas? It isn't giving us a check engine light.
Wendy