tonight driving the truck noticed when sitting at the 50km mark that it was shudering like it was going in and out of gear let it slow down stuck my foot to the floor and it went through the gears fine tryed it slow same thing when it hits the 50km mark seems to jump in and out of gear .
Just had and oil change and added an engine flush about to weeks ago used about 1/2 the tank of gas that it was added to anybody got any any clue
2000 f150 triton 4.6

 

Maybe the shuddering is really a coil pack going bad. As I remember my truck would start running rough like the engine was shaking a bit. Hopefully you will get a check engine light soon if its a coil pack.

 

Here is a real life case for injector leakage that just happened to my truck.
Cold start after a day of not being used.
Smoke from the tail pipe and an engine miss.
Left it run and cleared up.
What happened? An injector leaked all the rail fuel into the runner of a cylinder that had it's intake valve closed. The 'slug' of raw fuel flooded the plug until the cylinder cleared. Time for injector cleaner.
Just some info to relate and think about.