If you’ve run the gamut on recipes, including trying box mix, you’re probably overbaking. Since none of the recipes are going to be exactly alike, you have to find what is exactly alike across the spectrum: the oven/baking tme. You should not bake cupcakes (or cakes) until they are completely dry. Especially with cupcakes, which are surrounded by that hot pan, that will keep baking for a few minutes after they come out.
Try taking them out of the oven when a few damp crumbs are left on the skewer- and use a wooden skewer, not a metal one. Always use the shorter baking time for your test time. Try taking one out of the oven then, cool for a minute, and break it open. If it’s done, it’s done and take the rest out. When you’re testing, bake one or two at a time in separate pans so you can pull one or two out and leave the rest in if you find they need more baking time.
Also, use light colored aluminum pans. Those dark, coated pans absorb more heat and bake your goodies faster and hotter. If you only have dark pans, turn the temp down by about 15 degrees.
Good luck, and don’t get scammed by the latest round of huge cupcakes ordered!