Powertrain random behavior

Hello,

When I create a new vehicle I start from a base Powertrain that is quite old (and probably that's the reason it does not always work fine) made of this:

Code:

        "powertrain": [
            ["type", "name", "inputName", "inputIndex"],
            ["frictionClutch", "clutch", "mainEngine", 1],
            ["manualGearbox", "gearbox", "clutch", 1],
        ],
        "gearbox": {
            "gearRatios":["$gear_R", 0, "$gear_1", "$gear_2", "$gear_3", "$gear_4", "$gear_5", "$gear_6"],
            "friction": 1,
        },
        "clutch": {},

        "vehicleController": {
            "lowShiftDownRPM":3000,
            "lowShiftUpRPM":4500,
            "highShiftDownRPM":2000,
            "highShiftUpRPM":6000,
        },

....

        "powertrain" : [
            ["type", "name", "inputName", "inputIndex"]
            ["shaft", "driveshaft", "gearbox", 1, {"connectedWheel":"RR", "breakTriggerBeam":"driveshaft", "electricsName":"driveshaft", "gearRatio":"$finaldrive", "friction":2}]
        ],

The very weird thing is that it works perfectly in Realistic mode, using keys to shift, while in Arcade mode, when it is installed in some mods, the game is not able to autoshift, it will stuck in first gear, while with other mods it is able to autoshift.
So clearly there is some other external dependency that makes the game engine to not autoshift, but I could not find it, comparing all the other jbeams. Anyone experienced the same? What could be to prevent autoshift??

Thanks,
T.