Looks like I've fuel issues. It takes time to realise, but she has definitely become more sluggish, and really down on top end power, particularly cold, and on veg oil. I switched the tank from near 100% SVO to about 70% DERV, and a lot of the go came back, which makes me feel fairly sure I know the culprit. A new fuel filter will be fitted shortly.
(This is one of the problems of switching to SVO after a prolonged time on DERV - SVO drag's all sorts of sedimented muck out of the tank and into the the filter. I went through two filters in the first 500 miles, now its probably getting on for time to change the filter again anyway, and the dirt has built up again. The problem gradually dies down provided there isn't a prolonged switch back to DERV, I'd expect a normal lifespan from the next filter.)
As I type
10 years ago