I have had this happen twice now to me and I can't seem to find anything on this issue by searching, though I'm pretty sure I've read some threads about it. My 2001 Excursion after a freeway trip I'll slow down and go to accelerate on a slower road and it will not accelerate past about 30 - 40 mph. The RPM's were at about 3,000 RPM's then finally at one point it shifted hard, but would still not accelerate, so I pushed the pedal to the floor and it shifted back down, but still stayed around 30 mph. At one point it sounded like the motor RPM's would raise, but the X would not accelerate. The first time this happened, I replaced the fuel filter and the air filter and it went away (so I thought). This time I just turned the truck off, then started it back up and it's run great since. Any ideas on what this would be? It idled really rough too when I stopped and put it in park (or neutral). Any help would be greatly appreciated. Should I just take it to a tranny shop? Is this a module or something that needs replacement or am I looking at a new tranny? One more thing....Labor day weekend I hauled my toy hauler (this is between the two incidents) and it had absolutely no issues and I did some steep climbs with it. I'm confused.

 

There's a lot of guys with automatics that report strange driveability problems with automatics had it fixed by replacing the VSS (vehicle speed sensor) on the rear axle.
It's a cheap experiment at $20.00 or so if you want to do the labor yourself.
Apperently it get's fouled up after a while and sends a bad signal. The ECU relies on that signal for a number of functions, including knowing when to shift gears.

 

For $20, that certainly sounds like it's worth a try.

 

Let us know if it worked or not.

 

Hopefully I can get to it this weekend. Thanks