If your fuel pump has been lagging, maybe the pushrod that drives it has gone bad. I have heard that high miler big blocks have actually mushroomed the pushrod at the cam end! The only way to get them out is to pull the cam. Then you have to push the pushrod in further and take a file to remove the flared out end. Once it has been filed down enough, it should back out.
If you cant pull the pushrod out with a strong magnet, you may have to pull the timing cover to take a look.