B26: I don't think the Supercharger mod works on the Marauder, or if it does, it's in a different way than it works on the vanilla vehicles, since Shift does very clearly speed it up (I can't determine if the Marauder is faster when you hold Shift down with the mod equipped than without).
The Fuel Saver seems to work on it. At least, I drove the same distance with and without and it used 2% vs 4% fuel.
The only other non-vanilla vehicle I have is the MD-500 and it's really hard to determine if the Supercharger works on that (just because it's very difficult to judge how fast you're going in it), but I don't think anything happens when I hold down Shift.
Edit: Also, the description for the Laser Pistol says it disables demonic regeneration, but the stats page for it says it doesn't.
(The stats page has a 0 for ranged damage too, but that was the same in 4.1.2, IIRC).