I was lucky with my 6.0 when the EGR cooler started to leak:
1. The work was covered under warranty
2. The failure was small allowing me to continue driving
3. I was local and able to take it to a dealer that is versed in diesel repair
It's a tough call whether to replace your vehicle or fix it. If it has served you well up to this point and is capable of the tasks for which you use it, I would be tempted to fix it since even an infrequent expensive repair is less expensive than new vehicle financing. If you have had trouble with the truck before (dependability) or it no longer delivers what you ask of it, this may be the time change it out (even though trade in value is less due to the failure).