Just recently got a 55 plate 1.6 diesel estate and was great until I filled up at a Morrisons petrol station. Then it went sluggish and hated hills, it was ok when it hit hills at speed but from a slow start I felt like it was driving a HGV!! Yet on the flat the speeds are fine - just hates hills.

Could this be from a bad case of "dirty fuel" but cant see why on flat its fine?? Soon as I noticed it was sluggish I added fuel from Shell which I normally get but had to use Morrisons one day as running low. But doesn't seem to have improved much - added Redex to no avail.

Could it be the fuel filter? Any ideas greatfully received.