Good suction doesn't mean that it's pulling enough, 4-5lbs. It still could be a bad/weak fuel pump. It can also be a bad/collapsed fuel line. I would check the lines, replace the fuel filter and fuel pump. There are two types of mechanical fuel pumps for an 89 4.2; one has the inlet to the front, one has it to the rear. Check your original and make sure you get the correct replacement.