This from Eric Biel:

I know there have been a few posts tracking the delivery of the new Chicago ambulances on the Ram 3500 chassis. The first of these appear to now be in service – Ambulance 31 is shop # C-252. 
Eric Biel
Chicago FD Ambulance 31 Ram 3500 chassis

Ambulance 31 is shop # C-252. Eric Biel photo