Sounds like your Dad is doing great! My mom was also just operated on 2 weeks ago tomorrow and is also experiencing some shortness of breath after eating to moving around and they put her back on O2 after a couple days off. I really feel that it will just be a matter of time for them to gain thier strength back and get back to thier normal stamina again. Keep encouraging him to do the PT even if it wipes him out!
Cheers.
June