Bruce Stage three treadmill test

My husband just took a physical for a certain trucking company. He had an aortic valve replacement in 2005. DOT made him take the Bruce Stage two treadmill test and the cardiologist stopped the test and said he had passed. This company's PA said he had to complete the Stage three test before hiring. DOT only requires the stage two. The company is a very good company to drive for. The odd thing is, the Dr. that gave him his medical card also works with this company. My husband called him and asked him to explain. Since his chart was at the other place the Dr. that certified him told him to call him on Monday after his chart was returned. The job involves hooking up a lot of hoses, so we figure that is why they are asking him to take the stage three, it goes for 9 minutes. The stage two goes for six. Why does everything have to be so difficult? My husband has just been recertified because he went on insulin and didn't drive for 18 months. I feel so bad for him, he has said " All I want to do is drive again and it seems like everything is a long process. Any ideas on how hard the Stage three test is? How can a company have more stringent rules than the DOT. Lord, does it ever end?