2006 Ford Expedition 2006 Expidition

I recently had touble with my truck. It started out bucking a few times while driving, usaully on the highway. I slowed for traffic and suddenly the truck bogged and a message came on and said "RUNNING IN SAFE MODE" the truck did not stall but, I had to shut it off and restart it to drive. The dealership said it needed a throttle body, so they replaced it. A few days later I had the same trouble and with same result "RUNNING IN SAFE MODE". The dealership told me the spark plugs needed to be replaced. a few days later the truck started bogging more and usaully when on an incline not giving it enough gas to down shift. Now the dealership replaced the all the coils (8). The problem still exsist not as often but still when on the gas going along smoothly on the highway. For all the above the engine light has always come on first flashing then remaining on until the dealership does work on it. Also the "RUNNING IN SAFE MODE" has come back on. A few friends an I can only discribe it as it feels like it caught between gears but, the engine light comes on.

Please help, it has costed me a small fortune.

thank you,