You may be able to reduce the angle by raising the tail shaft of the engine/trans. See if you have room for shims. If you can get it below five I would think it should be OK. When you think about it, recommended for a leaf suspension is 5 to 7, and the rear axle is not angled from being under load on deceleration or real light loads. So it doesn't sound as critical at 5 degrees as we think.