I have a peugeot 206 year 2000 (automatic transmission car) electrical prob?

I have a peugeot 206 year 2000 (automatic transmission car) electrical problem, It does not have any power it starts picking up after 40km and i have my foot to the floor. Also it only drives in 3rd and i can not climb any hills. it runs fine on the flats after it paases 40km. also it starts in any gear.
Already Tried:
I changes the valve body and transmission oil, replace the multi function switch. now it starts only in reverse now still no power. any help...

Optional Information:
Year: 2000
Make: Peugeot
Model: 206
Engine: 1300cc