well you say it runs ok on the flat but not when pulling away up hills and I think gumming up would cause a problem all the time. However it is possible, like a few other causes, and you might stumble across the correct answer but I personally prefer a more structured approach to fault finding. This is even more important with a car thats new to me and I like to check each of the engine systems so I know theyre correct and can then be crossed off the list....