99 durango has no reverse all other gears work

When you changed the fluid you most likely disturbed worn clutch dust in the fluid of the transmission and plugged the works.

When is last time you changed trans fluid and filter?

check the transmission fluid and change the fluid and filter

Could it be possible the coolant lines are reversed not allowing the trans fluid to reach the cooler? The pressure line from the trans pump can easily be identified by taking it loose and directing the fluid into a container.

Sounds like a lot of miles...any routine maintenance completed? Fluid, filter change? Your least costly attempt to fix would be to add a full bottle of Lucas Oil Transmission treatment to your existing ****** fluid...no drain is needed. Be sure to warm your Durango by driving for a few minutes before adding the whole bottle. This fluid will attempt to reseal and lubricate the ******. Hope this helps.

CHECK TRANSMISSION FLUID LEVEL.IF OKAY.IF YOU HAVE NOT ALREADY DONE YET TRANSMISSION FLUID AND FILTER CHANGE IS DUE AT 100000 MILES.IF ALL IS GOOD YOU COULD HAVE FAULTY TRANSMISSION RANGE SWITCH.HAVE TRANSMISSION CODE SCAN FOR TRANSMISSION FAULT CODES.

CHECK TRANSMISSION FLUID LEVEL SOUND LOW.TRANSMISSION FLUID + FILTER SHOULD BE CHANGED AT 30000 MILES..IF ALL IS GOOD.TRANSMISSION SHIFT VALVE ADJUSTMENT CORRECT.HAVE CAR SCANNED FOR TRANSMISSION FAULT CODES FOR FAULTY SHIFT SOLENOID OR PRESSURE SOLENOID AND TRANSMISSION RANGE SENSOR.

These transmissions are known for having problems unfortunately.If it drives in first gear thei it sounds like a broke spring in the valve body. If you are not familiar with trans repair this can be a task as there are lots of parts in the valve body.Also could be a bad solenoid on the valve body they have fine screens and get clogged real easy. On these transmissions it is best to change fluid as often as possible as they are tempermental!

Hope this gets you moving forward!

You may need to change your transmission fluid and filter.Reverse is the first to show problems when your fiter is clogged or fluid is low. Im assuming you've checked the fluid.The reverse bands require the fluid to travel the furthest.This is the cheapest way to start investigating tranny troubles.If, when you drop the pan you'll see a small magnet. If the magnet has a large amount of metal filings on it, you could have worn clutches.Some filings are normal but if they include a splinter- like texture, you've got damage.

I think checking the transmission fluid level, and perhaps a fluid change with a filter change would be first step.

However, with only 68K miles on your vehicle, seems like too low of miles for the fluid & filter to be in that bad of shape unless you are driving in extreme dusty conditions, pulling a trailer, or other harsh conditions.