3.0 firing problems

[DALLBRIGHTAL01]

I have a 1992 ford ranger with the 3.0liter v-6. i have replaced the dist., coil, wires, plugs, o2 sensor, cannot find a vac leak, maf sensor clean, new cap rotor, the truck has a miss @ low rpm's. the truck ran fine until the distr. decided to call it quits. the timing is set correctly etc. i am out of ideas. the truck has 400,000 plus with good compression and power. the number 5 & 6 does not seem to firing as they should? the computer codes are saying i have a lean condition? can anyone please help?

 

[Runnin'OnEmpty]

Check for a leaking brake booster diaphragm, hose, or check valve.....

 

[DALLBRIGHTAL01]

I will check, any other ideas?

 

[Viper Command]

exhaust leak on bank 2 before the 02 sensor, your fuel trim learn should be in the teens%, also check your egr. for the leak.