V-10 Excursion missing; no code or pending code

No plug wires on a triton motor. Depending on where the X was sold wen new it may not be equipped with some emissions monitors, that may be why it's not setting a misfire code! Did you replace all the plugs? I would also recomend replacing all the coils and boots. Especially if you have alot of miles on it!

The coil on plugs are the spark plug boots. There are no plug wires from the plug to the coil like old style engines. If there was an interruption in the electronics causing a plug misfire, it should have thrown a pending code. The plug is getting consistent spark, but is is missing.

What is also possible is that the economy software causes it to hold a higher gear., but the winter blend ethanol laced fuel doesn't have enough power to accelerate at that low of an RPM.

I've got seafoam in it now. We'll see.

Or even the plug wires. Those Resistive plug wires will increase in resistance over time resulting in low spark. If you have the original wires, they are long pass due for replacement. If you've already changed them, forget this post.

Did you change the spark plug boots also? That is usually the problem I run into. The plug boots go bad and short out on the head. It does not give a code for the bad plug boots.