The P-38 kept the turbos, but exhibited unacceptable reliability in the European theatre at high altitudes
They didn't do well
but it's a little unfair to isolate the V-1710 as the sole reason, it is also remarkable in just how long it took Langford Lodge to get off their asses and correct the various problems with the implementation of field mods.
The altitude that the P-38s were being called upon to operate at were unprecedented to date, they seldom fought above 30,000ft and had not been forced to fly for long hours at those altitudes, this exacerbated several issues:
1. Windscreen defrosting
2. Adequate cockpit heating
these two issues combined to create the single biggest factor that diminished the effectiveness of the P-38 in the ETO. As for the engine problems:
3. Automated engine controls didn't appear until the H model; in the hands of an inexperienced pilot it was easy to overboost the engines on the throttle.
4. Supercharger intercooling design caused a number of engine failures, a simple redesign for the J model negated the reliability issues whilst producing more power from the same engines.
5. Being driven by all of this was the morale issue during the winter of 1943-44. Col George Doherty, CO of the 50th FS was apalled by the attitude of most P-38 flyers that they expected every mission to be their last.
When asked, a 20th FG pilot conceded "Well, those Allison 'time-bombs' didn't help any. That's the term we commonly used when referring to our engines. And there were many cases of frostbite. The lack of adequate cockpit heating went far beyond simple discomfort at those altitudes; it was enervating in the extreme".