I am having a problem with some of my cakes sinking in the center after I remove them from the oven. Is this from underbaking? ingredients? type of cake mix used?

I find that sometimes when I overfill my cake pans, this happens to me. Maybe you're pouring too much batter? Have you tried using cake strips? Many people say this helps the cake bake more evenly, instead of the edges baking faster than the center. I also find that some of the DH (if that's the brand you're using) mixes sink in the center and leave a gooey like mess on top. I never have a problem with the rainbow chip, chocolate, or white - but the banana supreme was terrible. Tasted good, but I had to trim a LOT of the top off. HTH

I found that happened to me when I baked my cakes @ 350'F.
I now do the following to prevent sagging:
1) bake all cakes @ 325'F (especially chocolate)
2) use a flower nail in my sheet cake pans on anything bigger than 9x13
3) use a flower nail in my round cake pans on anything 10" or larger
4) allow to cool in the pans 5 - 10 minutes before putting on a cooling rack

I use DH all exclusivley with no problems at all. Try putting a flower nail in the center. This will help because the nail heats up and helps to cook the cake from the center out. I do this for any cake 12" or larger and it works every time! HTH!