Johndeere 8875 starting problem

I have an 1996 8875 I am the original owner of the machine . It has 4200 hrs on it and it has a problem when it sits for more when about 5 days it starts hard like its lost it's prime if u run it every day it starts like a champ. Once it running it runs like it should any one run into this problem ? I replaced all fuel lines to injector pump and there doesn't seem to have any fuel leaks . I was wondering if injectors r leaking down when sitting