Highly likely. In addition to straining mechanical equipment, heat also causes slight deformation (kinks) in rails, a potential safety hazard, which is one reason that rail owners impose heat orders to reduce speeds.
Also, in the Northeast, the heat also causes problems with the overhead catenary lines. For example:
http://www.nytimes.com/2010/07/11/ny...o-north&st=cse
Theres a laundry list of reasons why Amtrak underperforms across the country, and unfortunately most of them are infrastructure-related, and thus very expensive and politically unpopular to fix.