S-10 Problem

[jayjbird1]

Hi Im a new reader I have a 1996 S-10 with a 4.3L vortec v6 with 150000 miles i have hade this truck sence 1999 and have hade very little trouble with it up untill lately it surges going down the highway at a stedy speed and i have gas coming out of the canister purge valve at the back of the truck and when it acting up black smoke comes out of the tail pipe and the tach drops 500 rpm, every now and then it will die if you are going slow and try to turn the check engine light comes on every now and then and the code is it's rich on both banks, I have changed the fuel pump, all the 02 sensors, the gas cap(it failed emisions), the mass air flow sensor, the coolent temp sensor, the injectors (spider) with the regulator, the truck also has a slight heasition when you take off from a stop light any ideas on what to do now