I had the same identical tranny problem on my '98 Ranger 3.0 at about 120.000 miles and changed the fluid etc to no avail. I took it to a really good shop that had been in business for over 35 years. It was fixed with new first gear clutch packs and a valve body gasket. It was considered a partial rebuild and cost $900. I have had 2 instances of erratic shifting since in 25000 miles. Both of these times were in very hot weather after driving in city traffic for over an hour. | 
