2001 Other Ford Models NO POWER

WHEN AUTOMATIC SHIFTS FROM 2ND TO 3RD, THERE IS A BUMPING SOUND AND LOSS OF POWER..IT IS NOT THE TRANSMISSION AS HAD THAT CHECKED OUT....lOTS OF SMOKE COMES OUT OF THE EXHAUST WHEN ACCELERATOR IS PUSHED TO FLOOR...FUEL IS GETTING TO ENGINE, BUT SEEMS TO BE A LOSS OF POWER. NO ONE IS SURE WHAT THE PROBLEM IS, BUT OULD LIKE AN IDEA
PRIOR TO HAVING IT LOOKED AT.... IT IS A 7.3 FORD DIESEL ENGINE...