New to this game. Just got a great deal on a 2001 4x4 dakota, 3 in lift, 30in tires. or so i thought. The truck started off with a backfire through the intake when under a load or going up hill. Changed the plugs, wires, rotor, cap, mass air flow sensor. didnt fix anything. then changed the upstream o2 sensors and helped a little. It still pops every no and then. when going down the highway i have to shift into a lower gear because it seems to have no power. Any Ideas what to do next. Bigger gears in transfer case/differential?