I am a cake mix baker and usually have no problems but every once in a while a 9x13 cake will come out with a wet/sticky top and never dried so that it is nearly impossible to frost (I do make my own frosting). The 8" layer cakes don't do this. The last 9x13 cake was a BC cherry chip cake that was wet on top and dense and heavy inside even though the toothpick method, that I use every time, had few crumbs on it and appeared done.  It was so bad I threw it out.  I am a date checker and check the dates on everything so I don't think the mix was old and it was stored in a cool pantry.  Also, I use the same 9x13 pan. Anyone know why this sometimes happens?

Are you leveling the top of your cakes?  If you are and still have it then it sounds like they are not baked long enough.  This has happened a few times with me but once I level the top of the cake its fine.  Plus, once I level each layer I flip it over so the bottom becomes the top.

I have this issue with my chocolate cake...I use Hershey's perfectly chocolate cake recipe using Hershey's special dark cocoa...I just tried experimenting with adding slightly more flour to the recipe and it made a big difference...it was still slightly moist on top but not wet, and it didn't dry the cake out...I increased the flour from 1 3/4 cups to 2 1/2 cups.