1999 GMC C2500 CRANK POSITION SENSOR

I have taken my truck to the shop because it would turn over but not start. It was running fine and then it started to back fire and surge. Sometimes it would start now not at all. The shop said it they pulled a code of, I believe 336 they said it would need a crank position sensor. I paid them diag fee and replace the part myself. It still is doing the same thing.I have 12v at the sensor, I have 12v into the coil and out of the coil with the key on. I replaced the cap and rotor because of some corrosion on the coil wire connection. The plugs are new the wires are new. You can hear the fuel pump come on. I put some gas into the intake to see if it would try to start. Still same issue. Please help!