Please Help: 1999 GMC Jimmy starts and runs goon but keeps dyeing

Hi, Thanks for the last answer, However I am a little confused on the THE answer. you said to go back and start at the Timing Chain AGAIN, dO YOU MEAN TO SET THE CRANK sHAFT gEARS bACK TO THE POSITION THAT THEY WERE FIRST AT? tHE BOOK SAYS THAT THEY NEED TO BE AT THE 6 O CLOCK AND THE 12 O CLOCK POSITIONS SO i MOVED It from the 3 o clock to the 6 o clock. It started Right up and drove pretty good, if it was wrong wouldnt not run at all or atleaST RUN BAD? nOW THE dISTRIBUTOR IS A nON aDJUSTING ONE SO WOULD A TIMING LIGHT EVEN WORK ON IT TO SET THE TIMING? aGAIN IT IS A 4.3 lTR. v6 2 WHEEL DRIVE vORTEC MOTOR. pLEASE LET ME KNOW . tHANK yOU