I like the GPM's. They hold up well and the larger bodies allow for more oil so you have better damping.
Nitro definitely get one of the 3 channel radios. For the few extra dollars its worth it, especially if you get a truck that uses the 3rd channel.
That clicky you are talking about is probably too tight of a mesh. Make sure the engine is straight too. Sometimes the mounting holes are slightly off and that causes the engine to be a little crooked. You should be able to slip a piece of paper between the CB and the spur and have it roll through smoothly without ripping when the mesh is set right. The spur gear could be out of round too, Ive seen that happen before. Sometimes they just dont come out right from the factory. If the mesh is wrong though you are going to destroy the spur in no time. I would make sure its right before you run it at all.
Also check the brake pad. Sometimes that gets out of line and that can cause the clicky feeling too.