I have a 1997 c1500 with 350 engine which will occasionaly bog down and kickback severely during starting/cranking. I have installed new starter(properly shimmed),new battery, new positive cable,new ground cable. The problem is definately related to timing issues. I also replaced the distributer cap and rotor with heavy duty brass contact parts. I replaced the ignition wires with new premium AC delco wires. The problem does not occur often but when it does occur it is severe. I guess it could be a bad crankshaft position sensor?? Any help or leads will be greatly appreciated.