Ask Our Auto Mechanics

Question: 1993 jimmy, appreciate your time,please help if possible

I HAVE A 1993 JIMMY V6 4.3VORTEC AND THE FUEL PUMP WENT OUT! I WORK AT A DEALERSHIP AND WENT TO AUTOZONE TO GET THE FUEL PUMP, GOT IT PUT ON BY A TECH HERE, HE TESTED THE PRESSURE OF THE NEW FUEL PUMP AND IT WAS PINGING 100PSI, IT RAN FOR ABOUT 4-5MINS BEFORE HE SHUT IT OFF, SAID THATS WAY TO HIGH, SO HE TOOK IT BACK OFF, I WENT BACK TO AUTOZONE AND GOT ANOTHER PUMP, HE PUT IT ON, IT TESTED AT ABOUT 60PSI... NOW THE VEHICLE WILL SHAKE LIKE ITS ABOUT TO DIE AT IDLE BUT WILL NOT, WHEN IM DRIVING IT SEEMS FINE, JUST AT IDLE IT SHAKES AND IDLES ROUGH.. THE GAS MILEAGE IS CRAPPY AND THE EXHAUST HAS BLACK SMOKE COMING OUT SOMETIMES AND IS BURNING VERY HOT AND WHEN YOU LISTEN TO THE EXHAUST IT SEEMS AS IF ITS POPPING. DOES ANYONE HAVE AN IDEA WHAT IT COULD BE, NO CHECK ENGINE LIGHT, NEW PLUGS, SUPER CLEAN TRUCK, EVERY RECOMMENDED SERVICE HAS BEEN DONE ON THE VEHICLE SINCE NEW, HAS 99K ON IT.....PLEASE HELP!!