But it never comes as a wave of replacement machines. Units get new issued gear on a priority basis. It's never done all at once. They don't move in to Ft Bragg, for instance, and simply replace every gen set on post. You could have two like units, on the same street, and one gets its new gear, and the other not. It's all about priority. AMMPS is not new. And a long way from being completely issued. The last time I was in Graf, one unit I always look at, had a few AMMPS, but mostly TQG's. In Fact, the TQG's in Graf, way outnumber the AMMPS.
The longer it takes to replace the gen set fleet, the worse condition the generators for sale will be in. We NEVER spent a dime on gen sets due to be replaced. In fact, there is a document called the MEL. Maintenance Expenditure Limit. That document tells a unit how much money that can be spent on a gen set for repair, or code it out, (turn it in because it's not Economically Repairable). Some commanders use this to "accelerate" the replacement of outdated/old equipment.
Just about the time I stopped working as a contractor, the MEL for the DOD sets, ( from MEP-002A to MEP-007A was $00.00. There were still lots of DOD set around, and the Government wanted to speed up replacement. So we were tasked to TI, (technically inspect) all DOD gen sets. Write up EVERY fault and shortcoming. Naturally, any fault considered a dead lining fault, pushed the gen set into the "Non Economically Repairable category. If the units priority was high enough, it got new equipment.