Many of the persons who previously would have been diagnosed with PDD-NOS actually do not end up on the autism spectrum now, but more accurately belong in the diagnostic category of Social (pragmatic) Communication Disorder. Loosely, it's all the social communication and interaction symptoms of ASD, without the restricted/repetitive behaviors.
The neuropsych could be very helpful early on, especially in the hands of a good clinician, but with the understanding that the absolute numbers probably would not represent the actual potential of the child, just their current levels of function. (This, btw, can be true of any evaluation.)
A speech language pathologist can also assess pragmatic language, but you might have to point that out in the reason for referral, so a little more time is spent on that. It may be, though, that there are also other language issues which are contributing to social challenges.
Personally, I lean on the side of comprehensive evaluations, rather than piecemeal ones, but speech/language and sensory evals would be separate people from the neuropsych anyway, so you could start from there. (Neuropsychs typically only cover cognitive (IQ), executive function (which may include memory & attention), social-emotional, achievement.)
