1) Ball bearings (get them)
2) Use a zip tie on the servo saver...or better yet just superglue the whole thing (tighter servo horn for more responsive steering). If you crash all the time, then do nothing or a zip tie is fine. I use an old Robinson Servo saver I had around which gives me more tension/resistance.
3) FLIP those ball ends that go on the servo saver! This simple step removes 99.25 percent of the nasty bump steer on this truck. So instead of the ball ends going on top of the servo, they should point down!
4) Also, install aluminum spacers on the ball ends of the left and right steering axle. You will need a ball end as shown. Or, you can use extended-length ball ends by Tamiya.
5) I used .1mm, or 2mm, or .3mm shims to remove play in the front suspension arms (I prefer less shake and wobble)
6) In the transmission, add a shim to the metal diff gear plate (this supposedly addresses the "clicking" sound in the tranny).
7) I use anti-wear grease in the diff gear shown in the photo below. Grease the gear cavities. This is just enough resistance, withoutstuff flying everywhere in your transmission. I put the slightest amount of anti-wear grease on the differential gears, like imagine almost putting nothing at all. It's not necessary to put grease on the metal gears IMO. DON'T let this stuff get on the white gears, that is the main point. I also put the anti-wear grease on the shaft of the outdrive diff (shown in the photo) below. Do this carefully, and you get a limited-slip differential for more traction!

9) Forget the use of rubber "o-rings" in the diff or rear axle outdrives. They bind the transmission for the most part. You definitely don't need TWO o rings as suggested in the manual. Play with it for smoothness. I have only one O rubber ring on the rear left outdrive. I think having no o-rings anywhere on the diff axles is perfectly fine actually. Your transmission will run smoother IMO.
10) There is an 850 size bronze bearing modification (it comes with your truck...assuming you have a spare since you installed ball bearings above) should your outdrive axle popout. I show you where to insert the metal bearing to push out the diff drive so that your axle doesn't pop out. I didn't do this modification because I don't have this problem. If you love jumps then maybe this axle popping out is an issue for you?
11) Replace the rear suspension spring with a slightly softer, or shorter, spring option. This will remove bounce and stiffness from the rear.
12) Be careful about tightening things too much in the rear suspension trailing arm...they have a tendency to create other issues.
13) Add a bronze bushing (850 size) next to shims as shown for wider track in the front and less play. Tighten the wheel nut carefully so it spins freely.