Thanks for all the suggestions
The n.gut wasn't pre-stretched, so that's definitely something I'll try next. Using thicker gauge is also a nice idea, and I do recall reading many great reviews on co-focus as a cross. I guess that pretty much sums up what to tweak for the next string job:
1. Pre-stretch the natural gut
2. Use 16 gauge strings
3. Natural gut/Co-focus at 60/52lb
My Klip Legend gut started fraying after just two kick serves. That was a little disheartening, although I think (hope) it's just the outer coating that's coming off, and the strings will last many more hours. Next time I will try Pacific Classic or Tonic+.