thanks so much for the info guys. RDC was extremely helpful, responding to email in 10 minutes!!! I found his technique primer useful. I'll cut and paste it below. Now I'm left wondering whether the hook grip will work better for me. I have been using alternating but I think I'll give the hook a shot.
FROM RDC's Site :
The sumo set-up:
Approach the bar. Take one foot or the other; your choice as to which is most comfortable and depending on whether you are a wide sumo or a narrow sumo. The shin goes up to the bar, and toes tilted out 45 degrees or even more in some cases. Shins vertical, and knees slightly bent. Hands should be down inside the legs with the forearms touching the inside of the thigh if possible. As you push your knees out (like the squat), you bend over slightly, with arms straight, and grasp the bar half on and half off the knurling. Your arms should be straight vertically from the shoulders to the bar. This rule will determine exactly where the hands are to be placed. For a very big lifter with wider shoulders this may be all the way on the knurling. For most, however, half off and half on will insure the best and shortest pull.
The arms are straight, and the bar lies in the fingers, like it is holding a hook. Thumb should be overlapping one or two of the first two fingers.
The bar should "not" be squeezed. Rather, it should just lay in the fingers/hand. Only the thumb should be flexed, or squeezed, not the hands, not the forearm. If this is done incorrectly, most likely, the bar on a very hard pull will slip out of the hands. Also if the hands are rotated as you grip the bar, it will most likely slip out as the weight pulls down, and pulls the rotated hands back to a straight up and down position. One does not have to have a strong grip to hold onto large amounts of weight. I have a very poor grip and grip strength and have never lost a deadlift, i.e. 716 at 165lbs.
The sumo attempt/pull:
As you are leaning over the bar knees pushed out, you dip the hips slightly to start your pull, short and sweet. The hips will pull in towards the bar. The head will follow from down to out as you start the pull. You will pull the slack first out from the plate/bar. Then, the bend in the bar slack will come next. The bar will pull into the fingers even more as this slack is pulled out and as all the different areas of slack are pulled out you will explode up, with a very short in line stroke.
The back will not be arched but have a slight curve in it/or perhaps even straight. You should take a short half breath right as you go down to the bar. Too much breath expands the chest and rib cage more than it need be. It raises the shoulders and lengthens the distance the bar travels, as well as forces the shoulders back while at the bottom right before the pull.
A variation of the slow sumo pull is the drop and grab and explode method. Everything is still the same as far as the hands, but it is done very quickly. Many times, when done too quickly or out of control, one grabs the bar wrong and/or the hips rise to fast, giving way to a stiff legged deadlift.