The History Channel has a piece on Lindberg helping out P-38 pilots in the Pacific, showing them how to stretch their fuel without damaging the engines.
Correct. Lindberg also offered to both join the army air corps, then act as an advisor. FDR turned him down on both occassions on accounts of the virulent anti-Roosevelt and isolationist speeched Lindy gave in the late 1930s up until Pearl Harbor.
He got 700 miles more combat range. That made the Island Hopping campaign where they didn't invade every island.
It also made it so the P38s had enough range to shoot Yamomoto down.