When my girls have minor tummy issues I add a small amount of pumpkin to their diet. It seems to help, but I haven't found scientific research to back up the benefits of feeding pumpkin. I use organic canned 100% pumpkin when I don't have time to prepare fresh, but NEVER pumpkin pie mix.
Here is a link to an interesting AKC read about dogs, diarrhea, and pumpkin:
Pumpkin for Treating Dog Diarrhea - American Kennel Club