I am not sure what the standard rates are on the stock springs, but it definitely sounds like you should at least bump up the oil viscosity and try heavier springs.
I am not sure how the Maxx trucks handle with RC Raven springs, but if these springs are anything like the triple rate springs they make for my Savage you will be in business.
http://www.rcraveninc.com/category/t...alratesprings/
$13 for a complete set of springs in various colors, it is definitely worth a shot if you ask me.
3ppi at the top and 7ppi at the bottom should allow your truck to keep the soft suspension to soak the smaller bumps but still allow your truck to handle some decent sized jumps too. It also won't have as much body roll as before too, and that means it will be less prone to tipping over when turning.
They helped out my Savage a lot (Savage springs have three rates 2.0, 2.5, 3.0 ppi for a total load of 7.5 ppi.), so I can only imagine that it will help you. I saw a huge improvement with just the springs alone. Just buy some heavier weight shock oil and add the springs and I bet you will see a difference.