Good Mornig Sir

My car is Santro Xing XO. There is a problem while driving. In plain/flat road there is no difficulty, but in a slanding road...my car can't perform better. When car is entering into a slanding road suddenly slow and make difficulty to run forward. So now I am so confused and tensed, please give me an effective advise and details about this problem..!

Yours faithfuly
Ratheesh