If the shorts were the only totally new change made, it seems logical to think they could be the problem. The gel sounds like it would be comfy, but I know I've never had luck with any kind of gel, be it in the saddle or the short. If you try them again on another ride and the same problem occurs, I hope you will be able to return them.
Annie
Time is a companion that goes with us on a journey. It reminds us to cherish each moment, because it will never come again. What we leave behind is not as important as how we have lived." Captain Jean Luc Picard