Possible vacuum causing my problems?

I drive a 1997 Chevy K1500 5.7 4x4. About a year and a half ago I replaced the fuel pump. Starting immediatly following the swap my engine started running real funny. It has a rough idle when started cold, a little sluggish in lower rpms and blows black smoke out both tail pipes (true dual exhaust with twin cats). I have tried different things to make it stop but have been unsuccessful (new plugs, wires, fuel screen with the pump, fuel filter closely followed pump, pump relay, seafoam in the fuel, oil changes and a few other things to no avail). I recently bought an OBD 2 scanner and paired it with my phone. I found that my O2 sensors were maxxed out and that my fuel trim was very VERY high I have read that a leak in the vacuum system can cause this. I am thinking back to when i replaced the pump and think i may not have checked or fully connected the vent hose that connects to the canister in the engine compartment. is it possible that something this simple could cause all my woes?