Ashley Karst

Son owns a 97 chevy silverado c1500, the previous owners had the cat cut off and put straight pipe with a glass pack. He started having issues with accelerating, truck back firing, not enough gas, and is always at high rpms. They have changed the plugs,wires,distributor, rotor, cap, fuel pump, fuel filter and a couple more things. Ran great until he hit some rough tracks and now its doing the same thing all over again. Engine light is saying 02 sensors and the down stream ones are not plugged in but I dont think that is the cause of all the issues, or could it be? Any advice would be great.