Here is what I have:

I have a 2003 Durango 4WD 5.9l, automatic transmission.
I have had this problem since last summer and it will occur for a while and then just go away.
What it is doing, is losing first gear. Sometimes it will take off in first gear but not shift back down into first, staying in 2nd.
Also loses the passing gear when this occurs.
It may do this for a few days, or a few hours and then go back to shifting just fine, maybe for days or even weeks.
I have changed the transmission fluid, with the proper fluid, and the filter.
Today, you could feel it seem to shift out of first and go into second while sitting still in drive, and it would shift back and forth on it's own.
I have no idea what to look for, is there a certain speed sensor, or a solenoid or what that I can look at replacing to solve this problem.
I had just put this truck up for sale because I thought the transmission was okay after it didn't give me any problems, but now I need to fix this
really quick before I find an interested buyer. I am going to have to take this off of the market until I can fix it,
so I need some major help quick.

 

Do you have a ck engine lite on? If so, what are the codes.

 

Does not give any codes, no engine light.

What controls the shifting on these transmissions, i.e. on other cars you will have a modulator valve,
what takes the place on the Durango's, and should I be looking at any speed sensors, is there a lockup solenoid??

 

Transmission Output Sensor. Drivers side about half way down on the side. It is very easy to replace. About $30.

Also you might need to have the trany adjusted. About $150 bucks if you don't know how to do it. I know how but still have my trany shop do it for me. It sounds like slippage so I would start with both of these.

 

Okay, I replaced the output speed sensor on the side of the transmission, did not fix it.
If this is an "every now and then" type of problem, could it still be in the band adjustment,
or are there other sensors or solenoids that I need to look at??
Like I said, the transmission could be fine for days or even weeks, and when it loses first gear, it may do it for hours or
even 2 minutes. [&o]

 

When my tranny was stuck in 2nd and not go back to 1st gear when slowing to a stop, it was a little low on tranny fluid. Filled it up and it is shifting fine.

 

Inside the trans there are metal rings. Since you changed the filter and didn't notice any bits of metal in the pan I would think that these rings are cracked and not holding their shape all the time thus causing your problem thus the slippage, as it was explained to me once.

 

iknow its a long shot but there is a spring on the trans that puts tension on the throttle cable that goes to the trans nmake sure thats all good