"I do like the idea of having more challenging assignments, but it is ridiculous that I get these tough jobs and excel in them while my peers are wasting away doing less difficult jobs and doing them poorly and still make rank at the same pace."

Honestly, you need to stop worrying about stuff like this and be the best officer you can be. There's little you can do to affect the career of another peer (other than diming him/her out and that's worse) so focus on what you want out of the military, and where you'd like to see your career progress to. The Army is seriously hurting for LT's and CPT's - they are going to promote almost everyone for the near term - and there's little you can do about it.