P40s takes awhile to get to speed.
once it is up to speed, it is a nice bird.
I usually grab to around 14k, then level out. it takes almost 1 sector for it to get up to speed. it is a good diver and turner, for a couple turns, anyway.
the slow acceleration is the main reason, it rarely RTBs.
My 1st kill, when AH2 went live, was in a P40b against a P38. I went on and killed a spit, then RTBed. I was the 3rd or 4th one to land kills, at the time.