1989 Ford E350 5.8 conversion van

have just purchased a 1989 ford e250 conversion van. It has apparently been sitting for several years. The mileage is 59,000. It stops running after 5 miles. I have had it towed 4 times in the past 2 weeks. Each time, it only ran for 5 miles. It would barely start but if left for an hour it would start again. They have replaced the computer, the distributor, the starter, the ignition, the battery, the fuel pump and filter, the ground wire, the battery cables, blew out the fuel lines and here I am stuck again. Can’t check the codes as the diagnostic connector is bad. Any ideas please?