I see where this particular thread goes back a few years, but the question does come up now and again.
Smokky1---you have a very good sinker, and that is what a "heavy" ball is. Ted Williams once described Spud Chandler as having a very heavy ball---and he had the devil's own time trying to hit it. Chandler, one of the Yankees' top pitchers in the late 30s and 40s, was a sinker-slider pitcher, and one of the best. So, if you've got a "heavy" ball, make the most of it---a pitch like that gives batters conniption fits!
I don't think anybody has ever been able to throw a ball perfectly straight; every pitch has a least a little movement on it, so you guys have no cause to complain. You might have reason to worry if you did throw a perfectly straight pitch, because that is what batters are always looking for, something they can really tear into and give a good ride out of the ballpark. But if you are able to get the ball to move one way or another, you're all right. As for the arm slot---the arm angle---you jujst want to stick with whatever is comfortable for you and what enables you to throw strikes and get those delicious outs.