Pumpkin Bread

So here's another fun pumpkin recipe!  I actually made this twice, and if you take a look at the picture, the bread sank down in the middle.  It did this both times I made it, and I can't figure out why!  Both times it rose like a regular loaf of bread in the oven, but as soon as I took it out and it started to cool, it completely collapsed in the middle.  My husband said that it tasted fine, but it doesn't look good.  I sliced it into smaller pieces just so that it wouldn't be noticeable that there was "sinkage" in the middle.  I will be making this again sometime soon so that I can see if we can make it look like a real loaf of bread...  If anyone has any suggestions, feel free to let me know!