FYI
My personnal read is that the M113s represent components for 3 mech Divs (+) and the BTR4s are part of 2 more Mech Divs [1 in line but 2 in command vehicles]. Existing other APCs are enough for a 6th heavy div.
The shortage is tanks and support.
The ordered/optioned 280 M1A1s only equip 1 Mech Div + a ACR [56th Bde].
The existing T72s/T55s equip a second Mech Div.
That means they need to order another 800 tanks to pair off with existing and inbound APCs. My bet is they will continue to order 140 M1A1s every 2 years and will add Oplot/Yatagan tanks from the Ukraine in the alternate years.
They appear to be concentrating on APCs first.
Note: Only half of the 6,000 M113s being retired are accounted for so far. We only started this final phase out in 2008. More may end up in Iraq/Afghan/etc. Giving them away is cheaper than scrapping with EPAs rules. Being replaced with Bradleys in combat roles and Strykers in support roles.