You've been full time 4 years. Have you signed up on the 9.5 list? I know it's not necessarily a cure-all, but it could help some. Start making 8 hour requests until you max out. Take R/O's when possible, use your sick days when needed. Should have what? Four weeks vacation? Work on managing your time off to allow yourself as much time to heal up, and rest as much as you can on your days off. And if you have any weight you can lose, work on that, it should help with the knees. I'm down around 20 pounds since I started driving, and my knees are doing much better. You've worked hard to get where you are, and I hope you can make it pay off and maintain your health.