[GSDsForever]

These are couple diets some EPI dogs recently have done well on:

Forza10 Legend Digestion (Actual Fiber ~1.5%)
https://www.chewy.com/forza10-nutraceutic-legend-digestion/dp/209890

Sport Dog Herding Dog Elite
https://www.sportdogfood.com/products/herding-dog#ingredients

Both are grain-free. You might try adding both lean protein + low fiber veggies (e.g. zucchini, squash, asparagus tips) and a very very small portion of a carefully chosen whole grain, to lower the percentage fat + carbs (while keeping protein high) AND be grain-inclusive. Mushrooms, are also low fiber, high protein per calories, and varieties like Maitake, Shiitake, Reishi, Enoki, and Turkey Tail/Trametes Versicolor are very good for cancer and the immune system.