Looking at your bump map I see you have made the panel lines and rivets subtly different from the base grey in order to avoid the effect being too stark. This isn't the best way to do this. This is because although there are 256 shades of grey available in the bump map the game does not read 256 variations of level from it, I'd guess its more like 16 or 32 levels of bump. The problem with using subtly different shades of grey is that sometimes the game will treat them both as the same level of bump.
A better way to tone down the bumps is to edit the P51D_B_d.txt file. The last line of this has two numbers and the second of these is the one you edit. If it has for example a value of 0.250000 it means the maximum bump (black to white on the bmp) will be three inches (0.25 of a foot). So reducing that figure to 0.025000 would make the biggest bump 0.3 inches. You can then make your blacks and whites on the bmp a lot more vivid and they will be read by the game but not cause massive bumps.
I'd suggest looking at one of my default bare metal skins' specularity maps to get an idea of the shades I use. The P-47D-25 or Ki-43 for instance. Basically though anything painted will be dark grey and anything bare metal light grey. Also dark panel lines and any shadow effects should be transferred to the spec map. Looking at your last screenshot the anti glare panel looks far too shiny. With that area turned much darker on the bump map than the bare metal it will kill that shine and look much more realistic.
I linked my old
bare metal tutorial in your "working in layers" thread. Its a bit out of date as AH didn't have spec maps then and the material.txt shown is invalid for the current game, but for painting the basic skin its worth reading.