I have a 1997 GMC Sonoma V6 4.3 L Vortec that has 140,000 miles, recently started having poor acceleration / hesitation problems. "Service Engine Light is ON" First found bad spark plug wires replaced, ran good for a while, problem came back and recently was informed 1 of the fuel injectors was defective replaced all 6 however. Ran good for a bit but still the Service engine light is on. Manual states emssion control problem, just looking for other possible problems.