what can I do different, my cornbread dressing was a little gummy? The moisture seemed right.
You may have added a little bit too much liquid, causing the cornbread to break down its usually crumb-like texture. You can try baking it the oven to dry it out, or even add more cornbread, albeit in chunkier, larger pieces.
I second ImmaEatThat's suggestions. Break the cornbread into 1-inch sized chunks and dry it out in a low oven, crumbs and all.
Did you add too much white bread?
I've always done a mixture of homemade corn bread and a white yeast bread (I use store-bought french bread). All the ingredients except for the stock get mixed in a large bowl, and then I ladle on the stock until everything is only as moist as a damp sponge. It only gets one or two good stirs to check for pockets of dry bread--a lot of recipes call for the dry ingredients to be tossed as you gradually add the liquid so that the result is moist but fluffy. Gumminess usually is caused by a little too much liquid and a lot of overmixing of wet bread.
My Thanksgiving stuffing/dressing has not changed over the past 20+ years, but the next time I need dressing I'm going to try it with a yeast-raised corn bread recipe I've been playing with. If it turns out well, I'll add the recipe to the food52 collection.