I agree, the engine braking on the Raptor is pretty poor. I came from a Taco, roughly the same size engine (3.5 L E'boost vs 3.4L 5VZ-FE), but a substantially lighter truck. Engine braking on the Taco was pretty good, the Raptor not so much. I think it comes down to the physics of the amount of energy contained in a moving 6k truck vs the compression/resistance that the E'boost can generate. To slow it down, the energy of the moving truck has to be dissipated somehow, either as heat in the brakes or energy consumed in overcoming the resistance of the engine. Even with fuel flow cut off, the E'boost just doesn't generate enough 'resistance' to dissipate all that momentum energy. I've locked out gears 6-10 more than a few times on long downhills and haven't really felt a lot of braking. Not sure I'd want to spin up the motor much beyond 4-4.5 K for too long unless I could feel my brakes starting to fade.