Go over your service records to see what has been done previously. Look in your owner's manual to see what is recommended but I would start off with changing all the fluids, engine oil, transmission oil, brake fluid if it has not been flushed withing the last two years, have an inspection done of the brakes steering suspension, tires hoses and belts. Tell the repair shop you choose that you are taking a long trip. Get the service done soon don't wait until the last moment just in case anything more serious is noticed.
This is the Factory recommended Maintenance Schedule for a 2004 Durango with 90,000 miles:
Change engine oil and engine oil filter.
Change rear axle fluid.
Change front axle fluid (4X4).
Check transfer case fluid level (4X4).
Inspect brake linings.
Inspect engine air cleaner filter, replace if necessary.
Replace spark plugs.
Inspect PCV valve, replace as necessary.*
Inspect auto tension drive belt and replace if required.
Drain and refill automatic tranmission fluid, change filter (3.7L).
Drain and refill automatic tranmission fluid and change main sump and cooler return filter (if equipped) (4.7L/5.7L only).