98 Grand Caravan, 198000 miles. 3.8 engine. Transmission pulls good until shift to 2'nd gear then slips. Checked codes and got generic p0734 improper 4'th gear ratio. Changed filter and fluid. Fluid was burnt, but no excessive metal in pan. When it starts to slip you can stop and put it in park then back to drive and it slips. You can back up about 50 feet and put it back in drive and it will pull hard until it tries to shift again. Help!