I was not satisfied with the stock rear shock on my DX450. The shock has no threads on the body for spring adjustments, replacement parts are limited, and the bore is too small to handle such a heavy gyro in rear wheel. (Note: with full weights the stock gyro is about 536gr which is over 1 lb for a single shock of this size!) I read a lot of comments back when this bike first came out that a Traxxas Revo shock works nicely. In fact Ive seen it used as a replacement in larger 1/4 scale bikes like the Ricky Carmichael rc dirt bike.
Whats really nice is the shock is almost a direct bolt on replacement. I was able to take the the bottom shock mount off the stock shock and thread it onto the Revo shock shaft. The Revo shock has more travel than the stock shock so I used some fuel tubing to limit travel. The top cap (mine is plastic) fits perfectly onto the upper frame mount of bike between the two e-clips that holds the shock in place.
There are different springs offered but I used what others suggested – the “blue” coded spring and it feels like the right choice. Theres plenty of piston options to test out too, unlike the stock shock. Im not a shock guru so I just used the stock piston. Depending on the gyro installed (e-gyro, aluminum, or stock steel version) and surface you drive on, the weight of oil is hard to suggest but try between 900-2000cst. I wish I could be more informative but I just haven’t used the bike as much as I originally intended. I purchased a single used revo shock for $15 so its an inexpensive mod. I don’t have many photos to post for this because it was just so easy to do.