Span & pitch is very much a personal thing...due to 'feel' every person is different. You need someone that is qualified to not only watch you but be able to interpret what you are feeling. If you feel your ball speed is slow, it can be caused by the wrong weight bowling ball to an improperly fit bowling ball, causing squeezing or gripping which creates a muscled swing which is generally causing a deceleration to let go of it. The grip should facilitate the ability to 'hold' onto without the necessity of 'gripping' and gravity creating the release at the proper position in the approach

I'd take Rico's advice over mine if there was a conflict or difference, but I'd agree with what he said, and maybe postulate a bit.  That span is awfully long.  Realistic, because I've had a few customers with hands that big, but it's very rare for a span to be over 5 inches with a correct fit.  Ideally, your thumb socket should be directly above your thumbhole, this allows your thumb to be straight in the hole and to come out of the hole straight on release.  If a long span is pulling your thumb slightly out of the hole and your thumb socket towards your fingers, it forces you to grip to hold onto the ball.  That also doesn't sound like enough reverse for the span, but that also reinforces a suspicion of a span that's too long. 

Depending on how your thumb bends, double jointed or other issues, normally if you put your thumb comfortably deep in position, the first joint of your middle and ring fingers should be close to 1/8" or 3/16" inches past the edge of the finger holes when you lay your fingers on top of the ball. Thumb pitches are determined by how flexible your thumb is. A quick check is= if the center line of your thumb lines up the closest crease line of your palm to the fingers when you fold it into your palm, you probably need about 1/2" reverse. This  NOT exact and you really should visit your local "pro shop" for proper fit. Also hole sizes are important to keep you from squeezing or "knuckling" the ball.