I was having the same issue with the flapper not staying up long enough. I checked the bottom of the flapper and the plug on the underside wasn't in correctly. I made sure there was no water in the flapper and put the plug in correctly. Now it works perfectly.

And we thank you for the update Jason. Tom

I am not an expert and i think the solution has not been resolved. I bought a 3-pack of korky flappers. One of the 3 worked. The other two dropped early and one leaked. I don't know what the solution is. I have been trying to figure out the reason for some time baring in mind the above mentioned solutions. Thanks, brad gilton