You guys do well 👏
I only achieve 17 on my local runs which are stop start, up and down hills, also short with a cold engine barely getting warm (that's my excuse but a heavy right foot may have a bearing on it).
On a run this only goes up to mid to late 20's but these are not motorways but frequently drivers roads.
Despite that no-one buys a 4.3 V8 and expects economy, well I certainly didn't. Its well worth it as it makes me smile every time I go out in it.
Ant