Gravy granules are not particularly lowcarb as they usually are made with starch and sugars.

Better to use the meat drippings/juices (if there are any) and add cream and xanthum gum to get the consistency you like.

Here is a recipe from Linda's lowcarb recipe site for chicken gravy

http://www.genaw.com/lowcarb/chicken_gravy.html

I tend not to make gravy but use sauteed onions/celery/red peppers processed into a puree with some cream/butter added to make a sauce instead.