Just to clarify, the P38 does not have dive brakes. The 38L had a dive flap that was designed to help the A/C recover from a dive that was approaching compressibility. They will not slow you down in a dive, rather they will merely pitch the nose up somewhat.
In the game the SBD, D3A, JU87 have dive brakes.
(never really fly it does the JU88 have them?)