I used to work in a butcher shop. When you buy burger at the store all those white bits aren't fat, it's sinew as well. Meat tasting like cardboard, sounds to me like you have a moisture problem--try med-rare. I take most of the silver-skin off my steaks and roasts b/c of tenderness and chewy bits(for the wife) but really the only silver skin I have to take off is the leathery strip off the center of the backstrap.
I just noticed you were from FL. where thedeer hardly reach the size to become a roast, your steak is my stir-fry...... your roast is my steak.... w/venison. I have cut hundreds of thousands of lbs of meat, made hundreds of thousands of lbs of burger and probabley a thousand lbs of sausage. Try again w/ somebody who doesn't know there a$$$ole from a hole in a ground.
Whats your fat mix for sausage or even burger? I think you have a problem! If you own or workin shop then I apologize and I think your customers are getting more than they paid for..... or maybe less. BAckstraps to burger, is that what you say?, thats like tenderloin to jerky!