my truck would not go over 15 mph and is knocking

My suv stated idling funny yesterday, then when driving I would give it gas and it would not go over 15 miles a hour. It made a knocking sound and the check engine light was blinking. It still runs but I had it towed so it would not get worse. I give it gas and it does not drive, check engine light blinking, making a knocking sound when give gas. I have it serviced regularly. I called a mechanic that said it COULD be the fuel pump that is located in my gas tank at it would cost 600 just to look. Is there a fuel filter on this truck, I could not find it????