2000 ford expedition when I drive it jerks like the engine is missing

is the motor missing or is the transmission slipping. if the motor sounds in time then I would say look at the transmission.

Do you have a check engine light blinking when this problem occurs? I assume you do because if it is missing and sputtering like you say the engine control computer would detect that and turn on the check engine light. Next step is to have the systems fault codes read through the diagnostic port under the dash in front of the driver, Autozone and others does this test for free.

Likly vacume leak. does it have the 4 litre straight 6? if so spray aero start at nr 1 & 2 intake to head & see if rpm changes.

It does it more uphill because the engine needs more fuel. Its starving. How about replacing the fuel filter.

sounds like valve train noise and engine is missing. Check engine light on?

Have you checked the spark plug wires?
They tend to cause this when conditions are right (or wrong), especially when heated up or cold and damp. If your mechanic checked it only when warm, not hot they might have overlooked the matter.

check pass side rear plug the coolant hose the runs to the heater core can leak coolant into the rear spark plug boot and cause a miss

ignition missfire ,most likely ignition wire

You may have a failing Mass Air Flow sensor, a quick test is to unplug the connector and drive the truck, if it runs better well their you go, the way this works is that the engine processor has failure mode strategy build in, so it substitutes a good signal for the missing one. After that just clear the codes and replace the sensor. The other issue may be fuel pressure, check the pressure and make sure it is ok under a load, a new fuel filter would poss. cure the issue also.

If you had the transmission replaced, it is possible that the spline was not lined up right, i would take it back and tell them to fix it....