From what I can see, the JLTV will replace the HUMMV, likely, on a one-for-one basis.
GHQ's AMPV looks like the XM1283 General Purpose (GP) version and that is supposed to replace generic M113A3 APCs. There are five other variants: mortar, medical evac, medical treatment, command post and engineer. Where you have a regular M113 in a TO&E, you should be able to replace it with an AMPV. However, it is a bigger so maybe it isn't a one-for-one replacement.
The
congressional research service report on the AMPV said the breakdown for M113s in a brigade combat team is:
Table 1. M-113 Distribution in ABCTs, by Variant
M-113 Variant Type Number of M-113s
M-113A3 General Purpose (GP) 19
M-1068A3 Mission Command (MCmd) 41
M-1064 Mortar Carrier (MC) 15
M-113A3 Medical Evacuation (ME) 31
M-577 Medical Treatment (MT) 8
So there aren't a lot of general purpose M113s to be replaced.