I've always baked my cake tall in 3" tall pans and slice in half to make 4 layer cakes.

Recently, my cakes come out a little differently.

They are... gummy? Not gummy texture like overmixed batter but they look very like mud cakes.

For my larger sheet cakes, I bake 4 single layers in 2 inch tall pans and they come out perfectly.

Why is this happening?

I like my cake recipe but I acknowledge that it's not very forgiving. 

Should I rather bake single layers but 3 layers not 4?

Are you making cakes from scratch or mix? Esither way, the quality of ingredients is down the road... That might be the cause!

Could be a couple of things. If not over mixing, it sounds a bit like under cooking a touch or maybe cutting before completely cool.  I use 3" Pans and lower my cooking temp (I have an electric oven)  by 25 degrees and cook a touch longer.  For clarification, I do scratch recipes, and found  that If I slightly under cook I had a slight gummy issue at times.  Same with cutting before completely cool.  Just a couple of thoughts.

Do you weight when filling the pans?  Maybe you get different amounts of batter in the pans.