Can anyone tell me the symptoms of a failing fuel pump?

I have had erratic sputtering that seems to come from the rear of my 84.

Is very distinct when the car is cold. Seems to get better after warming up.

The symptoms I am feeling are when I drive the first few blocks and step on the brakes to slow down for s top sign the car sputters hard with loud clunks coming from the rear. When I stop at the first red light the RPMs drop almost to a stall and I have to keep a foot on the gas while at a red light.

After maybe 10 minutes of driving the hard clunking from the rear stops. The sputter at a red light sometimes happens but not frequent. But I do have dropping RPMs on rare occasion that I still think is fuel pump related.

I replaced the fuel pump 2 summers back with a no frills fuel pump I got on ebay. I'm thinking its junk and misfiring. This was installed when I converted to dual exhaust and needed to pull the 2 fuel pump setup and retrofit to a 86 and up set up.

If I do replace the fuel pump what is the best option? I'm not pushing major horse power so I don't need a high volume pump. I still have stock CFI so I just want a good quality replacement.