Maker are you able to change D shifts to Tues/Thurs/Sat? Would that help any? I have been on that roster and that helps me spend more time at work (doesn't that sound funny?) being that I can get 3 full week work days in and 2 half days. Of course my work would be cool if I did Mon/Wed/Friday because I just have an awesome boss who would never put "requirements" on me like that, but maybe shifting D might help you better achieve your work goals? Just a thought.
The law is on your side with regards to disability. Start a file now and keep track of everything in case you ever need it. I'm glad you are able to get back to work because if you can continue to do it, work is good for you.