You can get any number of shots out of a barrel,but like everything else in life,you may get more,or you may get less!
It doesn't sound like you have loaded 'em hot,so it just might be a case of that barrel coming to the end of it's useful life.Have you thought about getting the throat extended .020"-.025" ,to see if that changes anything,it can be inexpensive to try this before getting a new barrel fitted.To determine how much to extend it by, get a chamber cast done.
A good rule of thumb is about 3000 shots before throat erosion gets bad enough to open groups.It looks like you have reached that point if your groups are opening,but you may get another 2000 rounds at that level before they open again.An old way to bring groups back was to increase powder charges (safely) until your groups tightened again.
The theory behind this is that the throat being eroded ,the chamber is essentially 'freebored' and charges can be increased because there is usually a drop in pressure,and therefore velocity ,when the throat has elongated.
I don't know if this is true or not,I have always re-barreled when I have reached this point in barrel life.