I have done twice baked many times and never had them come out like this… where they are gooey when mixed with milk and butter. Any cure?

It may be the variety, hard to say. But the Russet Norkotah is a moister tasting Russet potato and can sometimes turn out a little wet when baked, instead of dry with a crumbly texture. Some people prefer this moist profile. The Russet Burbank bakes up pretty dry and fluffy. Once baked, return the scooped out mixture to a pan on the stove to cook out extra moisture and try adding the milk and butter hot and not over mixing. Below are a few recipes I suggest to try.