Did you smoke the backstraps whole?
I usually smoke a whole pork loin this time of year, but i use an actual smokehouse, not a store-bought smoker. The main purpose is for flavoring, not to cook it entirely. I just season the thing well with Creole seasoning and then hang it over a nice fire that is, ideally, a mixture of green sweet gum and dry hickory. I generally get it to where it is about a third to halfway cooked. We then bake it whole in the oven and slice it to eat.
It would be interesting to try that whole process with a whole legnth of backstrap but with a much lower heat, and for not nearly as long, then bake the thing until it is about medium in the oven.