I remember your threads!
Fecal - regular poop check
You can do a PCR Fecal (that was a new one to me - I think there is a thread about it) http://www.idexx.com/pubwebresources...hea-panels.pdf
12 hour fasting GI blood work through Texas A/M
Any chance of overfeeding?
From that you should get some good answers. If it's IBD, that's a whole different thing that would need to be looked at differently, but I would guess you would start ruling things out doing the things above first.
But - you need to stop with the enzymes on an undiagnosed dog - contact Texas A/M to see if there is a washout time so that the blood work you send them is accurate. Be sure to tell them what kind of enzymes, how much and how long you've used them. Gastrointestinal Laboratory - Texas A&M Veterinary Medicine & Biomedical Sciences
I got my GSD at 8 months and her weight has not changed significantly since then (she's 10 now).