Ford Focus Mk1 Losing Power

[JamieMarchant]

Hi guys, so my mother in law has just given me her old Mk1 Focus to tinker with and sell. 
 

It appears to have an issue losing power when going into 4th gear uphill. To the point where it kangaroos sometimes. After reading through forums i pinpointed the potential issue to be the coil pack or oxygen sensor, which have both been replaced now, but the issue persists. 
 

Any ideas of what the issue could be? And if it’ll be cost effective to fix it anyway? It’s got 7 months MOT left on the car so would seem a shame for nobody to get the benefit of that, but obviously I don’t wanna spend so much on it that I’m only making back scrap value. 
 

Cheers guys.