lately i've been hitting 4-6" right of where i'm aiming. after paying close attention to my alignment i've improved a bit but now string slap is a problem. it's really anoying to shoot a group where you don't want to.

Are you torquing the string slightly...too much third finger pressure, or pulling it out at release?

The other thing to look at is  back tension.  I notice that if I fully engage my back muscles (even slightly more than normal/comfortable) my elbow goes back bit further and throws my alignment out and arrow spine goes weaker.  It doesn't take much.

Are you sure your arrows are not too weak in spine? Or are you canting the bow too much to the right?

i've got a nagging suspicion that they are slightly weak. i padded out the riser about 1/4". that seemed to help. but i don't know if it is because it stiffened the arrows or because the arrow now rests more to the left??

Padding out the riser makes the arrow act stiffer.  Back in the day this is how we fine tuned our arrows...build out with small pieces of masking tape to move the arrow inches at the target.

Try a lighter point weight to see what happens too.  That will stiffen the shaft.

Aim left.

How does making the tip lighter make the arrow stiffer,  not questioning you, just asking.

Imagine if you had a brick tied on to the front of the arrow.  When you shot it, the arrow would bend a lot before it began moving the brick forward.  Imagine if you had no point at all on the front of the arrow.  The arrow wouldn't bend much when it was shot, because it wouldn't have the inertia of the point to overcome before it started moving forward.  The amount of bend in the arrow as it is shot is a measure of the dynamic spine of the arrow.

Aside from tuning issues, a loss of back tension during release(collapse) and the resulting pluck are prime suspects when arrows impact to the right for a right hand shooter.

Having all the back tension in the world, does't mean squat, if its not maintained until the arrow is out of the bow.

McDave................that's an easy explanation!!  

Ben