How to power up MOC-0308, based on Technic 8297 Off-Roader? I have built the following MOC, with details here and here.

It is pretty complete, although I would have tried some servo motor for steering.

But after I've finished it, I've got into trouble:


Wheels on one side of the car seem to work sporadically. Could this be related to the steering joint and Cardan joint below?





Or the differentials?

 (image taken from Is it possible to create a differential if I don&#39;t have it as a ready to use element?)


It's too weak.


A wool carpet of 2cm thick is an insurmountable problem for the car to climb on it and go, especially for the last wheel or pair of wheels that have to pass the carpet's border (and difference in level), regardless which ones have to do it (back or front).

Are there too many differentials? Too many tooth gears? Too much elastic parts to deal with the torque? I can't find parts blocked.

The driving ring 2L, 
,
at the page 28 of the building instructions, should act as differential to switch between 2 x 4 and 4 x 4.

Could it be a defective motor? Is one XL motor too weak? Would be more powerful with two motors (in the back)? Which kind?

Batteries are OK for 9398, so it's not them.

Did anybody tried this MOC?

Sorry to have too much questions, it seems I need more experience with LEGO Technic.

UPDATE

I have changed it consistently, adding a gear down for each wheel (horizontally) and that made it 4L longer.

Also, moved the steering motor in front and the up/down and winch motor in the middle (switched their places), using a servo for steering.

As result, it is a bit more powerful, it climbs the carpet now, but I need to work more on the steering because it is not that smooth when it comes back in the default position. 9398 is better at going back to the default steering position. Also, 9398 is more powerful as it gears down 3 times instead of one.

Overall, the new design feels better, yet too lazy.
The piece you show must have steering axle 92906.