How do u know its a transmision problem?
Whats the total km of ur car and model/reg.?
Please, first check all the spark plugs and its condition....maybe they were never changed.....My mira couldnt go past 20kph and people said transmision is gone, while only 1 of the spark plugs had died coz it was never changed since factory....i replaced all and car went fine....i hope ur issue is same....