Advice on power loss
 

I have a 1994,4x2, 302 with 165,000 miles. It started recently having an odd problem. After about 20 minutes of driving, it starts to 'stumble' at random intervals. The 'stumble' feels like shutting the pet**** off and then on again while riding a motorcycle. I have replaced plugs, wires (routed properly), rotor, distributer cap, air filter and fuel filter. I also installed a new accel super coil. The coil did make things better but problem is still there. I do not think it is fuel pump related, because as soon as it starts 'stumbling', i'll switch to the other tank, and the problem is still present. Any idea on where to look next. I did check codes and received a 172, but found many entries online on what that could be, but am not sure its related.