Brake pedal goes to the floor but I am not losing brake fluid
You may not be losing brake fluid, but you may lose your vehicle if you don’t get it repaired.
Have it towed to a shop to get it fixed or drive it to the scene o the accident.
+1 to all the above. A Yukon is rather a large vehicle to be driving without brakes.
That is the classic symptom of a bad master cylinder. As was already suggested, I think that you should have the truck towed to a repair shop.
Bad master cylinder or bad hydraulic brake booster.