Your engine symptoms are classic symptoms of an engine with poor compression.
Poor compression can occur from a worn out engine or one with damage to the sleeve walls or piston. Since your's is a new motor it's unlikely to be worn out so that leaves piston/sleeve damage. That kind of damage can be from something external (like sand) getting in through the carb or something internal like a wrist clip or ??????
You could tear the engine down and look for damage or, since it is a new truck, contact Duratrax about your issues.
As for aftermarket parts, I don't think there are any yet. The truck's only been on the market for a few months. If it proves to be a popular truck (which seems unlikely with the reputation it's getting) then I'm sure you'll start to see hop up parts being made.
As has been said, check the Monster Truck fourm. There are several threads on your truck there. I'll warn you though, most are not complimentarry.