I'd look at the SCV as well, but when you're going up a hill, the filter is much, much higher than the fuel tank so the pump has to draw much harder to get the fuel up to the filter. If you've installed a second filter, that will be the cause. If your primary filter hasn't been changed in a while, or it's recently saved you from a load of gunk from a servo tank, that will be the culprit.
In order, I'd look at these:
1) If running a secondary filter, fit a lift pump near the tank with a high flow rate
2) If the fuel filter hasn't been changed recently, do it
3) Examine the hoses for possible air leaks (hard to spot, a clear section of hose on the filter outlet is the best method)
4) Remove and clean the SCV in petrol, rinse thoroughly in diesel before reinstalling