Why is the transmission slipping when first started?

Why Is My Automatic Transmission Slipping? If you have an automatic transmission and it "slips" while you are driving it-that is, the car engine revs without the power going to the wheels-the most common cause (though not the only possible cause) is low transmission fluid. If the slipping is caused by low fluid, it will get worse as the transmission gets hotter.
Why Is My Manual Transmission Slipping? A standard ("manual") transmission uses fluid too, but leaks aren't a common issue; a standard transmission could lose all its fluid and never slip at all, though eventually it would lock up while driving down the road. If you have a standard transmission, and it's slipping-the engine revs but it doesn't transmit power to the wheels-the problem is usually in the clutch.
Further down in the article I discuss how to diagnose this problem.
Sounds Like Low Transmission Fluid to Me

do you have a transmission problem? if you press on the brake pedel with you left foot and press down far on the gas pedal with your right foot-does the car want to really take off! or does the engine just rev like neutral or slipping with no grip?

Automatic Transmission?

Sounds like it is slipping

No fix for that-has to come out
or at least look at data & diagnose why your
having the problem

It sounds as if your automatic transmission clutch pack is slipping. You could try changing transmission fluid, but sometimes that may make it worse. You're likely in line for a new transmission. It will continue to get worse until your car will not go at all, or it may only be worse in certain gears, depending on which clutch disk is slipping.

try getting a transmission service,might get you a little more life out of your transmission but at this point you need a new transmission

If you take your Foot off the GAS PEDAL, will it go into the next gear? Transmissions shift by using PRESSURE and Opening the Solenoids Passages.

You may have a Solenoid Problem or a Electrical Issue, Normally if it is shifting out of 1st and going nowhere, I would suspect a Solenoid issue.

You may has also broke the Sun Shell inside the Transmission. This is not a Troubleshooting that I can go very far with you unless I hooked up my scanner but what you need is someone to put a Scan Tool on your Expedition and see what is actually happening. Sorry to give you the Bad news but I think at the minimum, you are looking at dropping your Pan and changing out a Solenoid but you could also have a major rebuild also...

Sorry

Yes it is the clutch slipping, in high gear the greatest load is put on the clutch so that is when they slip the most.

Have the transmission checked. Sounds like it is slipping some.

SOUND LIKE TRANSMISSION IS SLIPPING.CHECK THE TRANSMISSION FLUID MAKE SURE ITS NOT LOW.ALSO IF TRANSMISSION FLUID LOOKS DIRTY DARK AND SMELLS BAD REPLACE FLUID AND FILTER.IF FLUID IS GOOD YOU HAVE.TRANSMISSION OIL PUMP AND FORWARD CLUTCH PROBLEMS.

I have the same car,,i think your automatic transmission is slipping,(check fluid),or if its a manual transmission,then your clutch is worn out.(replace)