Problem solved. The show was returning to *slide 1* instead of *position 1* within the Custom Show. The most recent occurrence of slide 1 was at position 29 in the custom show, hence the looping at the end of the show. I added a third informational slide at the beginning and just never referenced slide 1 after the first occurrence. The new order is as follows:

1,4,2,5,3,6,2,7,3,8,2,9,3,10...19

Thanks to my friend Chris, whose outside-the-box thinking solved the problem in minutes!