If the new clutch helped the vehicle climb hills, then I dare say that was money well spent. As for noises from the engine under load, I’m afraid that’s a job for somebody on the spot who can listen to the vehicle and make an assessment. The noise could be major internal problems or it could be something as simple as a loose heat shield under the car. Even a loose or worn engine mount can create all sorts of mysterious and expensive-sounding noises and rattles. Don’t forget, your vehicle came with a five-year factory warranty, so a major failure that is not the result of mis-use or general wear and tear (provided the vehicle has travelled less than 130,000km) is still covered by Isuzu.