2003 7.3 E350 SMB
I have run her at 13,000 in CO no issues.
When I had power issue we cleaned both intake sensor and exhaust sensor but that did not work so replaced with new and bingo running like a top.
Again I have not had elevation issues with my 7.3. I'm not going to win the Pikes Peak hill climb but I will and have made it to the top.