Lately I have noticed my cruise control not being able to hold speeds on hills on the highway and struggling at all speeds. It sometimes even just shuts off and the memory is gone to resume. It is getting worse and worse. Some have suggested dirty fuel filter or air filter. I replaced the air filter not long ago but not the fuel filter. What do you think is causing this? It use to be very good and strong. The Vortec 350 V8 has been great to me. She has around 117,000 miles on the engine. Thank you.