What is wrong with 1995 Astro 4.3 2wd fi?

I have over 250,000 miles.I cleaned tbi(egr,IAC, flushed hoses that go into heater.I have so much oil,etc that I degreased to be able to pinpoint new leaks,4th fuel pump that I know of,I've redone rear-end,u-joints,etc.Tune-ups by far hardest.Now it runs real rough,and bogging down,put sea-foam in gas,lil bit in oil,some sea-foam in tbi,no error codes(code 12 only)alternater sounds bad, hissing from dash penfer