'04 Excursion No power, won't shift into high gear

[gdwhetz31]

Hello,
We just purchased a 2004 6.o diesel excursion with 115,000 miles on it. For the last 2 weeks, it has ran great. This morning while driving to work, I heard a '"pop" and the the truck lost power. It will not go faster than 45 mph and it doesn't seem like it will shift out of 3rd gear...won't go past 2600rpm. It still runs smooth and sounds normal. It just doesn't have any power and will not shift into high gear...... any thoughts? We are planning on driving it 600 miles to Reno in a week.... HELP!

Thanks