1996 Dodge Ram no EGR and no catalytic converter

Engine Mechanical problem
1996 Dodge Ram V8 Four Wheel Drive Manual

it has no egr valve or port in the exhaust manafold has no cat cherry bomb dual exhaust, O2 sensors pre and post are in the exhaust pipe on the passanger sideonly the pre is installed I am sure it is toast. My problem is it has poopr gas milage like 6 or 7 miles to the gallon. It starts up instantly but when it is up to operating temp it harder to start.I recently discovered that vacuum port next to the MAP SENSOR FRONT OF THE THROTTLE bodygoes straight into the evap purge soleniod. There are two ports on the EPS one is vacuum the other goes to the evap canaster. The port next to the MAP sensor is piped to that other port on the evap purge solenoid what is the problem with this hook up. I need info on how to incorporate O2 sensor with the vacuum lines where they should be or what is the best I can do with no cat or egr vavle