Can someone please offer some advice on baking cake layers that have straight vertical sides?  Mine are shrinking at the top, which cause them to take on the shape of a donut...  I use an oven thermometer (my oven is a little hotter than the display reads) and lowered my temp.  It caused me to have to bake longer, which was okay, but I ended up with the same shrunken top rim.  

I also use bake-even strips, which help reduce doming but don't do anything to prevent the rounded sides.  

I've tried to just deal with it and fill the side gaps in with icing but that always backfires when the icing gets the slightest bit warm and the excess weight causes it to droop.  

I use Wilton professional pans that are straight sided.  They do not nest.  I've read just as many posts claiming that straight-sided pans yield straight sides as I have read ones that claim slant-sided pans are necessary to give cakes the shrinkage room that results in straight-sided cakes. 

As you can imagine, I'm at my wits' end...  Any advice? 

So, if I’m reading it correctly, are you meaning that your cakes are sinking in the middle, and pulling some of the cake in with it?  That in itself sounds like your cakes are underbaked or too wet.

I would just trim the outside of the cake before icing. 

how much water do you have in the cake strips -- I soaked mine and it took forever for the cakes to bake -- but they usually/never warped like that --idk -- you have an uneven bake going on -- 

by the way I bake at 350 degrees then at the end of the bake reduce the temp to 325 so the cake can keep setting up but not over baking in the already done areas -- but I also put a foil loosely over the top -- spray grease on it so if it touches the top it doesn't stick -- and i leave it on after I pulled the cake out -- especially for the big poppa bear cakes -- but if I overfilled a pan i'd have to do that too --

maybe try something like that --

also use a heating core or something like this:

I put the foil on at the end of the bake when the sides are clearly done and the middle is not -- some cakers bake at a lower temp altogether but I never liked the rise I got and the baking powders are calibrated to give the maximum punch at 350 so I start there and lower as I go toward the end --

I have a feeling it might be your recipe.  Maybe it has too much liquid?  Or you are under baking.  Yes, the lower temps do require longer baking times but in the long run you get a much better cake! :)   Instead of 350 or even 325 as most recipes state I always baked my cakes at 300 degrees F for about 20 minutes (for any cake using 1 cake mix batter) then turn it up to 325 for an equal amount of time - untilI can smell that wonderful aroma of sweet CAKE in the next room :)   I found I got a much more moist and level cake w/o that wasteful hump in the middle.  Also for larger (over 14" pans) I would use a flower nail in the center as a conductor of heat into the center.  Just grease the flower nail, place in pan then carefully pour in the batter.  When the cake is baked it's easy to remove the nail and the center of the cake is done.

Also, maybe if you could post a pic of what you are refering to we could have more ideas to help.

I bake at high altitude and occasionally have trouble like what you describe. I've tracked it down to incorporating too much air into the batter (like if you over whip the eggs), or if I don't slightly decrease the baking powder/soda.