I do not think that a tranny flush will resolve your issues or even prolong the inevitable (to have your tranny rebuild) A filter change and fluid change may helpa bit but again :( Here are some other possibilities. There are many causes of automatic transmission slipping as the system itself is quite complex in its make up. Here are some of the prime automatic transmission slipping causes.
Torque Converter Malfunction
Modern automatic transmission systems are hydraulic in nature and the power for driving the transmission comes through the torque converter. It is the torque converter which pressurizes the transmission fluid and provides hydraulic power to shift gears. A malfunctioning torque converter, with a reduced pressurizing capacity can be one of the main causes of automatic transmission slipping.
Transmission Band Problems
For the proper working of an automatic transmission unit, it is vital that the transmission bands are adjusted well. If they are not, gears can slip out of place and cause the transmission to slip.
Worn Out Gears of Transmission
Gears which have worn out along with warn out transmission bands can be the prime causes of a slipping transmission. Warn out gears do not engage properly causing the transmission to slip.
Drop in Level of Transmission Fluid
One of the common reasons of slipping in automatic transmission is inadequate levels of transmission fluid which adversely affects gear functioning and its shifting leading to slipping.