Ssangyong Korando Lack of power

[Bez]

Please help. My daughter has a Ssangyong Korando Auto with an intermittent lack of power problem. The vehicle drives beautifully for a while then just has no power. If Travelling on a straight or downhill it will maintain its speed but will not increase speed at all. The vehicle revs will climb but no response. If she stops just for a second the vehicle drives beautifully again. . Needless to say at times she prays for a toll gate!
This also results in really bad fuel economy,.
The turbo has been redone and the inter cooler cleaned. Now people are suggesting it is a gearbox problem . (Transmission) could this be? Other ideas are a blocked exhaust. Unfortunately it is too costly to repair by elimination. Has anyone has this problem? Where can we find a GOOD mechanic. In the Durban area ?
Please any feedback will be appreciated.
Korea does not reply!!

[Bez]

Sorted .Blocked exhaust!