1987 Toyota Supra MY Supra LOSSES POWER WHILE DRIVING

Engine Performance problem
1987 Toyota Supra 6 cyl Two Wheel Drive Automatic

hI 2 DAYS AGO MY DAUGHTER WAS DRIVING HER CAR HOME FROM WORK, IT WAS PRETTY COLD AROUND 15 DEGREES, SHE STOPPED AND PUT GAS IN IT ONLY FILLED HALF FULL, THEN PROCEEDED TO DRIVE HOME, IT WAS FINE FOR ABOUT A MILE AND THEN SHE SAID IT WAS SPUTTERING AND ACTING LIKE IT WAS OUT OF GAS, GOING REAL SLOW AND WOULDNOT GO UP A SLIGHT HILL SHE PULLED OVER AND CALLED US TO COME GET HER, WE THOUGHT IT WAS FROZEN FUEL LINES OR WATER IN THE LINE SO WE GOT SOME HEET FUEL ADDITIVE AND PUT IT IN AND IT RAN OK WHILE IDLEING, BUT IF YOU PUT IT IN GEAR TO GO FORWARD IT WOULD SPUTTER AND DIE. MY HUSBAND REVED THE ENGINE AND LET IT IDLE WITH THE HEET STUFF IN THERE AND AFTER ABOUT 30 MINUES IT SEEMED FINE AND WE DROVE IT HOME, THEN BACK TO TOWN TO FILL UP WITH GAS AND TO MY DAUGHTERS WORK ABOUT 5 MILES ROUND TRIP, IT WAS ACTING FINE RUNNING WELL SO WE THOUGHT IT WAS FIXED. SHE DROVE IT TO SCHOOL THE NEXT DAY AND IT WAS FINE, THEN ON HER WAY HOME IT DID THE SAME THING AGAIN? LOW POWER, SHAKING AT TIMES AND WOULD NOT GO MUCH AB0VE 25 MPH BUT SHE GOT IT HOME AFTER PULLING OVER SEVERAL TIMES AND REVING THE ENGINE. WE WERE TOLD IT COULD BE THE FUEL FILTERS? WOULD LIKE TO FIX IT OURSELVES IF POSSIBLE BUT MY HUSBAND IS NOT REAL MECHANIC MINDED SO CAN SOME ONE HELP DIAGNOS? THANK YOU SORRY THAT WAS SO LONG!