I doubt anyone can take some beef and run a test to tell you if it came from an animal fed GMO or not.
Typical grocery store beef comes from cattle fed at a feedlot for a couple of months. They tend to have a higher fat percentage which increases the tenderness.
When working on a cattle ranch in Nevada, the beef was butchered at the ranch from cattle on grain for a month. It was tasty even though it had a bit less fat than what I see at groceries. The main difference we could tell at the ranch was between a heifer steak and a steer. Heifer steaks were more likely to be tender though not universally so.
Typical grocery store beef comes from cattle fed at a feedlot for a couple of months. They tend to have a higher fat percentage which increases the tenderness.
When working on a cattle ranch in Nevada, the beef was butchered at the ranch from cattle on grain for a month. It was tasty even though it had a bit less fat than what I see at groceries. The main difference we could tell at the ranch was between a heifer steak and a steer. Heifer steaks were more likely to be tender though not universally so.