Hello murat,
Check the engine timing, as it effects engine vacuum. Engine vacuum, in turn, effects transmission function. Make sure that the vacuum connection from the intake manifold to the transmission is good. Also remove the access cover inside the car and check to make sure that the transmission linkages work. You may want to spray some lube on the linkage pivots.
The transmission linkage can be adjusted by using the turnbuckle. This will change kick down. I do not recomend you do this unless you check everything else first. Accurate adjustment of the linkages and the modulator pressure on the transmission should be done with a pressure gauge using the specs in the BBB.
What is the history of this problem? The solution may just be a simple engine timing adjustment. Start by setting the timing to 30-35 degrees BTDC at 3,000 rpm.