Hi again, very glad to hear there's progress, good persistence, too!
I would recommend making a back-up of your input map (in a different folder) at this point, before making any further changes.
As for the steering being slow, if it's the wheels react slowly to your input, I think that's normal (there is a setting to change it somewhere, I can't remember where, sorry), however if the steering is just not sensitive, there is a Analog Input Sensitivity setting in Settings > Controls. I'm not sure, but this may impact the pedals, too.
If you are on Windows, open the Run window (hold the Windows keyboard key and press R) and type in joy.cpl and hit enter. You should see your wheel on the list of controllers. Click "Properties", after which you should be presented with all the axes and buttons, try the shifter and see if different buttons light up. You may also be able to see what the sliders are controlled by.
If your shifter works by using buttons, then you can open the Input Mapping Tool and assign "TRUCK_SHIFT_GEAR1" (and 2,3,4,5 to) "TRUCK_SHIFT_GEAR6" and "TRUCK_SHIFT_GEAR_REVERSE" to the corresponding shifter positions. Set up the clutch pedal if you have one (TRUCK_MANUAL_CLUTCH).
As for the shifter/gearbox setting (Settings > General > "Gearbox mode"), you can try "Fully manual: stick shift" or "Manual shift : auto clutch" (if you don't have a clutch pedal). Pressing "Q" while in game, in a vehicle, cycles through the gearbox modes, so you can try them out that way, too. (this will later allow you to switch between paddle shifters and the normal shifter but we'll set those up after this)
If you are using the "Resume Game" option from the main menu, and already have a car spawned, you will need to delete it (CTRL+DEL) and spawn a new one (CTRL+G) for the new gearbox settings to apply.
I'm sorry if we're not able to address things like the throttle response seeming off. I'm not that familiar with RoR and don't even own a wheel, so somebody else who has experience may be able to help with this?