mice eaters are often slow growers it seems they just never get quite enough. It was just a thought about the F/T I am glad to see you have been trying options. One of mine is a backwards eater he also needs small meals. Fecals were clean? it really sounds like a parasite sometimes you need two clean ones a few months apart to be sure internal parasites don't always through off eggs or sections that can be seen in poop. There are DIY fecal tests if you have a microscope it isn't super hard, vet tests are better but cost more. Again just a passing thought. I have a slow grower (had) she was always fed F/T and never guessed parasites but in the end that was quite wrong she is much better now and much bigger.