we replaced my 1996 Chevy Silverado 4x4 truck engine with a new crate long block. everything went together but when we went to start it it acted up. weput the new engine together with new spark plugs, wires, cap and rotar. New water pump and air filter. tested the fuel pump was at 65 when we first started it up but would drop to 0. So we replaced the fuel pump. put 2 bottles of sea foam in it and its only running on four cyl. tested the spark all have spark. the only thing we can think of is the spider is bad? or the injectors are cloged? Help Please.