Park is not present because the transmissions themselves do not have a Parking Pawl physically in them..
the MD3060,AT545,MT643,Allison 2000 series (2100,2500, etc) do not have the park and hold mechaniscm.. you cant add a 'P' to the shifter for this.
the Allison 1000 has the provisions for a parking Pawl.. on Light duty applications like the GMC pickups and Vans(cutaway busses) the parking pawl is installed, the Medium duty applications.. (GMC 7500,8500, navistar BE series) the park pawl is Not typically installed but can be added or is optional;
thus why you wont find a full chassis school with a 'P'..
to park you place the shifter in 'N' and set your external parking brake.
-Christopher
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