99 Blazer Bad gas millage fast idle

1999 Blazer 4WD 4.3l I used to get around 16 mpg in town but it has dropped to 13 in the last month or so. A while back I noticed a bad smell from the tailpipe that I still smell from time to time. I have resently noticed when coming to a stop the rpm's hold around 1100 but drop to around 600 - 700 about the time I get stopped. So it feels like I am holding the gas while braking. There are no codes, fuel pressure is around 55 - 58 lbs. I have not gauged the vacuum but I don't hear a vacuum leak. I replaced the fuel pump about a month ago because it went bad but everything seems fine with that.

1999 Blazer 4WD 4.3l I used to get around 16 mpg in town but it has dropped to 13 in the last month or so. A while back I noticed a bad smell from the tailpipe that I still smell from time to time. I have resently noticed when coming to a stop the rpm's hold around 1100 but drop to around 600 - 700 about the time I get stopped. So it feels like I am holding the gas while braking. There are no codes, fuel pressure is around 55 - 58 lbs. I have not gauged the vacuum but I don't hear a vacuum leak. I replaced the fuel pump about a month ago because it went bad but everything seems fine with that.

Fuel pressure is to low.
Sounds like a airtex pump.
What brand pumpdid you use?
How is fuel filter.
Need 60/66 lbs of pressure.
Put a fuel pressure gauge on it and road test and watch pressure and post back pressure readings.
How is the tune up end?