One of the problems with the P-38 in Europe was that it suffered from an inferior heating-defrosting system. At high altitude during bomber escort missions, the canopy would fog/ice up and cause the pilot visual problems along with the distraction of trying to scrape it off.
Obviously, that was no problem in the Pacific.
Valid point about no/poor cockpit climate control. However, p-38s were used heavily in the Aleutians and I don't recall ever reading of engine performance problems in those cold, wet conditions.