Hi I'm new .. I have a prob sort of Chuggs when driving

Hi I have finally managed to save the money for a Freelander... Got 03 serengeti.. Few probs sorted but having probs with this.... When driving normally my car starts to sort of Chugg I keep thinking it will stop but never has... my mechanic is having a prob finding it, had service, recent new exhaust, head gaskit is fine, new fuel tank 3 wks ago.. I thought it was like fuel starvation but it seems not.. Clutch pedal also quite low.. and today warning hill decent light on... Please can anyone help advise.. Thanks

Bit more detail please, petrol or diesel

Hi its 1.8 petrol
Thanks