2000 Sierra blowing fuse

Good Morning, I have a problem with a Fuse that blows it is labeled inj-a
and will blow in a very intermitent way, some times right after installing it and other times it will work for a few weeks and then blow!!!!
We have replaced the fuel pump 3 times due to low pressure, but now we are completely out of resources, (pumps are 479.00 at the dealer!!)
any help will be great....