Other Fuel System Tank Filling/charging problems of the 1998 Ford Windstar

Problem originated immediately after purchase. Was taken in 3 times for repair. Fuel gauge would not register full when filled and filling up with only 12 to 14 gallons when at 1/4 of a tank or less. Problem supposedly fixed but still had occasional erratic movement and improper fuel gauge readings over a period of 1 1/2 years. Problem became much worse in July 2000. Had erratic movement in fuel gauge, would fill tank, gauge would go to full, then drop 1/8, then go back up to full, the drop 1/8 again. Filling up at 1/4 of a tank or less with 12 to 14 gallons again. Vehicle has been at dealers 5 times, to date. Continually say that it is fixed but when I fill up with gas the problem is still there.