I've got a similar problem... My drives off the tee aren't usually more than 200 yards (if I'm lucky) and are probably closer to 170-190... I'm finally getting them to go straight instead of a slicing fade due to changing my grip.
What I lack for in distance off the tee I'm trying to make up for in my short game. I occasionally am blessed with an phenomenal shot close to the green. I'm trying to improve there because I don't think my drives will be much longer in the future. If I think about more of a hip turn while swinging my ball goes into a banana slice.
Get a lesson. It costs what, the same as a round with a cart? I went through the whole routine working on my slice, analyzing it, making progress, having setbacks, when I was out of ideas, I got a lesson. Hit a couple good ones during the lesson, more the first range session and the half a large bucket on the second range session I spent on the driver had some really good shots for me, nice little draw, and an increase in distance. The only time I seem to hit the old towering banana slice is when I fail to concentrate and try to swing out of my shoes.
A good teaching pro can see stuff you are not even looking for. For instance, he took one look at my glove and saw I had a grip problem from the wear pattern.
One think I was doing when I was trying to ramp up my swing,like triggering it from the hips, was that I was lifting away from the ball, in an instinctive bid for more power. The pro pointed that out too. I didn't believe him at first, but I really concentrated on not doing it, and was able to start driving slice free with power. (well I am pushing 60, so carrying the 200 yard sign for me is plenty of power.)