The tester came out came out clean, but when I turned the pumpkin loaf out onto a rack, it fell apart. How do I fix this?

To fix it, maybe you can put the a cream cheese frosting on the middle and just say that this is part of the design.

Are you looking for a way to put it back together? or just prevent it in the future?
For the latter, you're going to want to let it cool in the pan for 15-20 minutes before you dump it out, not much longer, or it may stick terribly. But letting it cool some helps it set.

If you are looking for a way to "fix" this loaf, I'd say you're looking for pumpkin trifle recipes...