John Deere 455 low power at startup
 

I have a John Deere 455 diesel.... when I start machine up it takes 2-3 minutes to get to full rpms it idles with no throttle response.... for 2-3 minutes then slowly goes to full power still doesn’t seem to have full power but it can be used I have replaced the fuel pump screen in line filter as well fuel pump works fine go good fuel flow....glow plugs tested and work fine all 3... I have replaced all 3 injectors with aftermarkets.... I am wondering what to do next could it be the governor?? Still have an injector issue?? Was thinking of bad injector it would not right at all.... any help be appreciated....