Hmm, i assume you mean Ground Effect? This is where within about 1/2 a wingspan from the ground your wing generates more lift, since the air being pushed down by it hits the ground. Makes landings easier, and makes it harder to fly into the ground at low level (I noticed that it takes quite a bit of nose down trim to stay at treetop level now).
Prop drag will slow your dives down a little, I guess you could shut the engine down (auto-feathering the prop, if the plane has variable pitch prop(s)), but since you might need it at the bottom, that'd be a little silly
. Personally I welcome the added drag on landings, even though you might have to land with a little throttle on to lower your sink rate on final.
About the P-38, dunno. The P-51 feels better than ever, that's all I know
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Rickenbacker