Just a thought as I have no experience with the DR650 .
Your bike will have been running rich in the mountains , maybe the spark plug[s] are fouled - some bikes are very sensitive to this .
Your air filter could , as you say, be clogged .
Try the bike briefly without an air cleaner element and see if there is a difference .
Look for the simple stuff before you start pulling the carb apart .
Blessed are the cracked, for they let in the light. - Spike Milligan
"When you come to a fork in the road ,take it ! When you come to a spoon in the road ,take that also ."