1989 Chevy S-10 Fuel System Problem

I recently bought a 1989 s-10 blazer with a 4.3 TBI V6 4X4 and I was told before I bought it that it needed a new fuel pump put in it before it will run right. I was also told that the problem was intermittent with the fuel reaching the engine so a mechanic told them that they need to replace the fuel pump. They bought one but never put it in opting to just sell it and be rid of it. The vehicle came with the pump and my question is. Is it possible for the sending unit to also go bad or do I just need to replace the pump only or what? And is there anything other than just dropping the tank and popping in another pump that I need to know or do or something else I need to buy before all this will work? Thanks for the help!