Falling profits, muted outlook, aggressive restructuring -- that pretty much sums up Cummins' (CMI -1.32%) last year. Or should I say, it sums up 2015 for most heavy-machinery companies.

But Cummins has been among the biggest losers in the industry over the past year, falling more than rival Caterpillar (CAT -0.55%) despite a smaller exposure to the struggling mining and oil and gas sectors. In fact, Cummins also took a bigger hit than PACCAR (PCAR -2.26%), its key customer in the trucking industry.

CMI Chart

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Cummins is clearly under tremendous pressure, and there's little to suggest that things will improve anytime soon. Take a look at the slideshow below to learn about the three biggest hurdles to the company's growth this year.

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