Have it looked over by a trusted shop or dealer, maybe do some of the minor maintenance like serpentine belt, hoses, plugs, fuel & air filters. Inspection of brakes, tires, and running gear of course. I highly recommend a transmission service, and possibly a cooler upgrade. Google 6.0 transmission cooler mod. Maybe get a 2nd serp belt to carry with.
If you trust the EX daily, you shouldn't be wary of a cross country towing trip.
Our '03 has approx 109K on the odometer, and has done a 5000 mile trip back to the midwest towing our almost 7K Jayco, many 3-10 day mini-vacations in the mountains of WA and Oregon on many fairly steep passes. And will be going down to the Utah/Arizona area for a 30+ day trip in mid Feb. I don't have any worries about it doing the trip. I run Mobil 1 5W30, and change every 7500 miles or at 6 months. Maybe use 1/2 quart in summer towing between changes.
If your V10 has been maintained, and kept up with, it should be good for many, many more miles.
'16 Outdoors Timber Ridge 280RKS
Reese 1700# Trunnion w/ DualCam HP
'03 EXCURSION XLT V10 4.30 Axles