97 Chevy P/U MISFIRE

MY 97 CHEVY 1500 4X4 5.7 VORTEC HAS 160000 MILES ANDHAS A MISFIRE WHEN CRUISING DOWN THE ROAD IT IS RANDOM. THE TRUCK HAS BEEN IN AND OUT OF THE GM SHOP 4 TIMES AND THEY TELL ME TO DO THIS AND THAT AND IT NEVER WORKS IM GOING BROKE. IVE CHANGED IGNITION MODGULE, COIL, TIMING CHAIN SET, PLUGS THREE TIMES, PLUG WIRES THREE TIMES ALONG WITH CAP AND ROTOR. THE TRUCK HAS HAD THREE TRANSMISIONS IN THE PAST YEAR, THE DISTRIBUTER HAD A FLAT SPOT IN THE GEAR BUT CAM IS PERF SO REPLACED. CANT TIME IT WHEN ITS DEAD ON THE TRUCK WONT RUN BUT BACK FIRES AS YOU TRY TO START YOU ADVANCE IT AND IT RUNS GOOD BUT MISSFIRES RANDOMLY. PLEASE HELP ME AND YES CHECK ENGINE LIGHT IS ON AND THE CODE IS SAYING THE CRANK POSITION SENSOR IS FAULT OR THE CIRCUT IS MOULFUNCTIONING.I ALSO CHANGE THAT SENSER