It is not getting enough fuel for complete engine combustion. Check the fuel injection system.
Fuel injection system fuel trim too lean (Bank 2)
Fuel injection system, fuel trim to lean (bank 1)
That year don't HAVE a choke. Is your check engine light on ? If it is, then you need to have the engine scanned with an engine scanner to see what is going on. Problem could be the MAP sensor, coolant sensor,fuel pressure regulator. Any of these problems could be making it run RICH are LEAN. Fuel injection fuel system DID NOT USE A CHOKE.
engine will fit, but 305 tbi will be too lean for 350 It'll burn up
A vacuum leak could do that, also low fuel pressure or a dirty fuel filter.
Because that is when GM went to the first generation Vortec heads, and, they overcame injection lean issues.
Trouble code P0174 means: Fuel Trim System Lean (Bank 2)
Bank one is "LEAN" - get a good bottle of Fuel Injector Cleaner and see if that helps.
It sounds like some sort of lean condition. Perhaps a vacuum leak? Plugged fuel filter?
More information is needed. Please restate your question with specifics about the type of manifold, fuel delivery system, and carburetion. Also explain why you think the rear cylinders are lean.
Code P0175 Means Fuel injection system rich left bank Code P0171 means Fuel injection system lean right bank Code P0172 means Fuel injection system rich right bank