I'd take it to Slealth, Storm to name a few to have it sorted mate, it aint running right if it's that slow and doing those mpg, my last VR6 was standard and was pretty much the same as my mates 182 when rolling. They aint as fast IMO as a 2.8 should be they seem a bit lazy and need thrashing but they should easily beat the escorts and astras you mentioned, they feel slower than they are because they are smoother and less frantic than a 4 cylinder 16Valve motor. If I get another VR6 it wil defenatly be getting charged to make it what it should have been to start with.