So first on the build list is the differentials, of course. The TRF 801XT comes with sealed diffs, so you can fill with diff fluid to your desire. Being a newbie at truggy building and sealed diffs (and just a basher), I'll just slap in the supplied Tamiya silicone diff fluid and be fine with that.

Here's a pic of the parts to go into the diff build, and a few as I built it. Notice the spiral-cut ring gear. Nice and durable!