I will start by saying that this is not the first time that this issue has happened. At 164,000 miles the transmission started freewheeling in drive when you would go to leave a stop light. If you brought the revs way up and held them or pulled the shifter down Into 1 (much better option) it would engage solidly.
The truck in question is a 2000 Excursion with a V10. We took it to a trusted transmission shop and dropped the pan. No damage or problems were ever found. We drained and replaced the fluid and the truck returned to normal.
Fast forward 5 years and 110,000 miles and the truck has a variation of the same issue. If you reverse for more than a few truck lengths the transmission gets stuck in freewheel mode. Pulling it down into 1st will get it in gear unless you have reversed a great distance. Then 1st and large amounts of high rpms will be required for foreword movement. It has also once or twice while towing shifted into overdrive and just free wheeled. There was nothing there. I turned the overdrive off and we made it home. The fluid is full and looks fine. I have since drove it with no trailer and it locks into overdrive with no issues.
I have been reading up on the filter change and fluid flush and plan to do that this week. Any other ideas besides an expensive rebuild? My local shop wants $62 just for a diagnostic. ...

 

I would definitely do a trans fluid/filter change if you've only done it twice in 274k miles if my math is correct...

 

With how complex and expensive a trans can be, $62 is a fairly cheap option.

Mark K should be along here shortly, he's the resident trans guru.

 

Make sure you do a flush, not a change of the trans fluid. Should take about 17 or 18 quarts.

 

$62 is really cheap for a diagnostic. I'd be surprised if new fluid fixes this one.

Did you say you went 110,000 miles without a fluid change?

 

Yes it has been that long without a fluid change. I wish I had found this site years ago and realized how easy it is to do on your own. When you only drive the truck a few times a month and the transmission never gives you any trouble the miles kind of get away from you.
How many miles can you expect out of a transmission without a full rebuild?

 

I'm at 568,000 plus and still running good. I do a flush every 100,000 miles

 

251,000 with nasty slipping. Mine is an exception, I beat my truck like it owes me child support. With regular maintenance and care, it'll last you a good long while.

 

I have a 2005 Ford Excursion with 143,000 plus miles on it. The other day My wife and I were pulling our 30 Toy Hauler across Texas headed for Murphysboro, Arkansas. We had been traveling all day, so for about 8 hours. Not taking any interstate highways. So we were going through a lot of small towns. We stopped at a red light and the smoke started rolling. I pulled over to check it out and found that the transmission was leaking. Dripping right on the exhaust Y pipe. Therefore creating a lot of stinking smoke. But after about 1 minute it stopped dripping. I checked the tranny fluid level, and all seem good. I stopped at an auto parts store and bought a gallon of tranny fluid and headed down the road. It seemed like it would only leak when we stopped on a hill. We kept going and kept an eye on the fluid level until we reached our stop at the campground. Still smoking and stinking. Before we left to head back to home to Kansas which is another 7 to 8 hour drive. Anyway I checked the fluid level again and it was a little low. I ended up adding about a half quart of tranny fluid. It seemed to me to be leaking from the front of the bell housing. But not sure. Can anyone tell me anything about this? Can it be something else? Thanks!

 

I would start by checking the vent hose for the transmission.
if it is plugged for some reason it will force fluid out the dipstick and or the front main seal under load.
It happened to me. It would only leak when towing hard under a load.
We found the tube full of mud daubers!

 

What trans fluid did you get? MERCON V? MERCON SP? MERCON LV? You must use the right fluid for the transmission, and in 2005 the Excursion could have one of two transmissions.

Gas engine trucks had the 4R100 and the diesel trucks had the 5R110W. The 4R100 used MERCON V and the 5R110W used MERCON SP or LV. Using the wrong fluid could destroy the trans.

 

Yes mine is a gas V10. It has the 4R100 tranny. I bought the Mercon V tranny fluid.

 

I will check the vent hose to see if it is plugged. Thanks!

 

Also can you tell me where to look for this vent tube? I have a feeling that is my problem. Or maybe that it was overfilled?
Thanks!

 

The vent is on top of the trans, right behind the bellhousing. If it is a 4x4 there will be a tube that runs up the firewall. If it is a 4x2 there is just a vent cap.