OP,
If he was in the special ed preschool, will he still have an IEP/qualify for services for K? If he does, you may want to wait on the testing. If a diagnosis would actually net you something, e.g., services, special program, then do it now.
Either way, I would finding therapies outside of school to help him with the sensory/regulatory, e.g., OT.
For us the visits to the developmental pediatrician/neuropsychologist were the points where we were at the crossroads--we didn't know what the issues were or what the next steps would be. It sounds like you've taken appropriate actions and have a handle on what his issues are. Would a diagnosis at this point change what you're doing?