The distance from the toilet floor to the septic is less than 25 feet. I have snaked the pipe and have run water. All appears well. I put toilet paper in the floor hole and after I run water and take a shower it backs up through the toilet hole in the floor. What do you think?

Sounds like you still have an obstruction or the tank is full. Is the drain field wet? Cast Iron pipes only last so long. That's why PVC is great.