That thing needs a good clean, and a few other areas need some attention too:
Lock the tranny into 2nd gear, and install an RCM steel idler.
Change the front drive shaft to a 3.3spec item too, may need cutting to length.
Rear stiffener posts can be got from GorillaMaxx directly, just look in the spares section for the G3 chassis (will fit fine, as the thicker upper plate is thicker in the upwards direction).
Swap the plastic steering posts (they look plastic anyway) for the optional alloy ones, and then get yourself a nice Kimbrough large gas truck servo saver for whatever servo you fit.
Get a servo with atleast 200oz/in of torque ideally.
Should make for a nice project truck with all that in mind.