I have the cake mix doctor's book, but so many of her cakes are bundt cake recipes (I have no bundt cake pan). Every bundt cake recipe that I have tried to replicate in a round 8" has come out way too thick. What am I doing wrong? Should/can a bundt cake recipe be done in a regular cake pan?

Yes, you can use whatever size pan you want. Instead of one pan you will use 2 or 3 depending on how many layers you want. Be sure not to fill your cake pans more that 2/3 full.

Some cake recipes that are for bundt pans, actually do turn out better in either a bundt or angel food pan. This is because of the way they rise and the centre heating core that is actually built into these pans. Some recipes need a lot of support while they are in the rising process because of the leavening ingredients and this is part of the reason that they do well in a pan where both the sides and the centre provide support. Most of these pans are 10 inch, so like it was said, you likely have too much batter for the size pan you are using.
You will have to measure the amount of batter and put the correct amount of batter into your regular pans, this is about the most accurate way to go. Some recipes rise more than others and displace more space, so you will have to experiment.
I find that most bundt recipes will make 2 of the standard 8 inch, 1 1/2 - 1 3/4 inch deep pans, the old standard pans we used to bake with, not the deeper 2-3 inch ones we use now.
I also find that some of these bundt cake recipes do well in springform pans of a slightly larger size, the 9 or 10 inch pans.
Some recipes were designed specifically for a bundt pan and though they will still turn out, they do better in a bundt pan, cook more consistently, are able to cook through the centre at the same pace. The only way to know for certain is to experiment. I have a chocolate cake bundt or angel food pan recipe that cooks best in these pans, but I also cook in regular pans.
There are different sizes of bundt pans, some are 4 cup, some 6, some 8, so this is a factor also.
Sometimes the batter is of a thicker consistency and will do better in a tube pan than a regular one, but will still work in regular pans. The density or texture may end up slightly different though.
Hugs Squirrelly Cakes

Hi there, sorry don't have the book, I tend to make mostly from scratch types of cakes.
Just guessing here, but does it have about 4 eggs, a package of pudding, some oil or butter etc?
Bundt cake recipes are all pretty similar with one or two things thrown in and most of these cake mix books that are out there, are variations of recipes Duncan Hines put out at one time or another.
I don't use heating cores, upsidedown flower nails, or bake even strips, even though I have all of these things. I just have never had a problem cooking a cake without them, so I don't use them.
I would make it up once, measure out the batter to see how much it makes and then determine what sized cake pan to bake it in. You may have to double the recipe or adjust it to make the correct amount of batter you need for the size of the cake pans you want to cook it in. I use the Wilton guides for the amount of batter needed as a rough guideline, try it out once and then determine if you need a cup or so more or less for your pans as all recipes rise differently. Chocolate cakes generally do not rise as much as white cakes made from mixes.
If you have 2 inch deep pans, these are the easiest to cook in, to get the heat in the centre evenly.
What size pan do you want to bake in and are you trying to get one or two layers out of a recipe? Are you using a Duncan Hines or a Betty Crocker mix, generally a Duncan Hines produces more batter.
Hugs Squirrelly Cakes