Ok so you said you have "rotator cuff" problems and I don't think enough people are taking this into consideration. you must address that problem first. You cannot possibly push yourself as hard as possible with lingering pain and the threat that it could get worse. Being a pitcher for years, I know about rotator cuff problems. Try these tests and see how you match up. If you can't perform them properly, you need to increase shoulder mobility.
1) Stand flat with your back against a wall with your arms up at a 90 degree angle, with your elbows bent at a 90 degree angle. You should be able to keep your butt, legs, heels, shoulders, elbows, and hands in contact with the wall without too much discomfort. Don't arch your back either to compensate....someone should barely be able to fit a hand into the gap between your lower back and the wall.
2) Grab broomstick with your hands very wide, wider even than a snatch grip. you should be able to bring the broomstick up and over your head, rotating your shoulders as you do so, with your arms straight...touching the broomstick almost to your back before returning the same way. This is a great warmup and will get your chest opened up nicely.
Sorry the second one has a bad description I hope you get what I'm saying. These should be pain free.