Just bought a 2007 Navigator w/ 105k on it. Took it on a 1000 mile trip with no problems. Afterwards I went up a hill and had to gas it a bit. When it reached 4-5k RPMs the check engine light started flashing and I felt like the engine started shuddering a bit and lost some power. After about 15 seconds the light went away and haven't had any issues since.
Took it to an autoparts store to get it scanned and there were no codes in the history. My first though it the spark plugs because of the mileage, but I was also thinking it could be the fuel filter because it did it at high RPMs. I guess I might just have to replace both.
My guess would be a coil. As they start to go they can cause the engine to stutter especially at the higher RPMs when there is more load. I had this happen on my 06 F150 and it never threw a code, it would just cause the truck to shake and buck like riding a bull.
If the plugs have never been changed I would change them now anyway.