Stalls when put in reverse
 

2001 Expedition 5.4L. Trucks runs great. It doesnt matter if its warm or cold, it has a problem stalling out when put in reverse. I have cleaned the idle air control, then I put a new idle air control on it. Could this be the fuel filter? Torque Converter? Another question, possible relevant...when we drive the truck around town it doesn't leak, but recently we drove about 3 hours away and it dumped quite a bit of tranny fluid????:-banghead

check for vacuum leaks all around the pcv area and the intake. If it dumped a lot of tranny fluid, you should get it checked out immediately. Make sure it stays at the proper level! A low transmission fluid will cause this condition because in reverse, the pressures are higher than in drive. Again, if it lost a lot of fluid, you need to add it back. Truck should be driven for 15 minutes or so and park on level surface with the vehicle idling and check the level.

Maybe
 

Could it need a new PVC valve? I'm just praying it's not the tranny!!

Streetdoc

PCV valve is cheap. If you are leaking large amounts of fluid when the vehicle is driven for a few hours, you have issues...likely not the PCV valve.

1. How many miles?
2. Have you ever dropped the transmission pan and replaced the tranny filter?

#1 - you MUST use the called for Automatic Transmission Fluid. Anything else and you are asking for problems.
#2 - it could be the Torque Converter Solenoid failing. Again, I believe that in reverse, the TC is under more pressure. Maybe that is why you are only seeing this in Reverse and not just in idle.
#3 - check the fluid NOW. Engine running, level surface, engine hot! (drive 15-20 minutes)

Ok, I feel like an idiot. Adding just a little tranny fluid seems to have helped keep the truck from stalling. Any ideas on why it is dumping tranny fluid when driven for long distances?

The cooler could be clogged and overheating the tranny causing it to dump out the vent tube...or...it could be a seal that failed...hard to say unless you tell where it is leaking from.

Find out where it is leaking on long trips.

I'll ask again, when is the last time you had the transmission fluid serviced? (drain or flush?) What type of fluid did you put in it?