Ford F-150 2002 engine size 4.2 and mileage is 194,000

My husband recently replaced the spark plug wires and spark plugs but the engine lost a lot of power. When we try to drive up hills it doesn't have a lot of power. We have to shift back to 3rd to make it up hills. We hear popping noise in the hood when we stop and go to shift into 2nd. Before he replaced the spark plugs there was nothing wrong with it. The truck had a lot of power. Also we had it diagnosed it the codes says misfiring from cylinder 2-6, system too lean bank 1 and 2, AGR fuel flow excessive. He says he removed the wires one by one to replace them. So, any mix up is out of the question. Also, he put old spark plugs back into to retest it but didn't do anything. Same old thing. We can smell gas when engine starts up. Engine idles rough and doesn't have much power, also when you shift to first gear it sometimes engine will just shut off. We need help please.