Jeep has taken the new Grand Cherokee upmarket with the quality and ambience to match its off-road ability, says Matt Kimberley of the Press Association.

The Jeep Grand Cherokee is one of those cars you might think you know well enough to dismiss; but at the risk of spoiling the bottom line, the new one is something of a surprise.

It's moved upmarket with a new flagship trim level, better soundproofing, an eight-speed gearbox and, on the higher models at least, a whole new 'infotainment' interface from Harmon/Kardon.

All of a sudden the Grand Cherokee – historically the archetypal Jeep thanks to its size, simplicity and legendary thirst for fuel – looks a very different beast. For a start, the engines are changing and becoming much less eager to visit every filling station forecourt they pass.

Hence why the UK will see only diesel models, with the exception of a handful of monstrous V8-engined SRT versions. Only about 10 were sold in the UK last year – in line with predictions – but the performance leviathan is still a powerful marketing tool.

The next phase of the Grand Cherokee's 'Eurification' is the introduction of a new, higher, better-looking and comprehensively equipped trim grade.

It's called Summit, and it's what we're testing here. It comes with a serious count of bells and whistles, with heated and chilled seats, heated and chilled cupholders, a heated steering wheel that can be set to fire up with the engine in the cold months, full leather upholstery, a 19-speaker (including three subwoofers) Harman/Kardon stereo system and what's probably the world's most in-depth trip computer.

The computer's functions even extend to giving a 3D-effect map of the car's chassis and wheels, displaying both the front wheel turn angle and the state of the multiple differentials. It's a hugely useful set-up for proper off-road driving, which is something right at the heart of the brand's ethos that company bosses vociferously refuse to ditch. Every Jeep, they say, will always have genuine off-road ability at its core.

But it's on road where Jeep has tried to make the biggest improvements. The ZF gearbox plays a huge part, shifting smoothly and briskly up through the ratios in both the 'drive' and 'sport' modes. Revs are kept lower and the whole package just feels a lot more civilised than before, and this car's V6 diesel engine is quiet too, growling nicely under power but settling into the background at a cruise. eighth gear returns around 1,850rpm at 70mph.

If there are any black marks they come via the boot and the steering. The former could be bigger if not for the presence of an (admittedly essential) spare wheel and tyre, while the latter is vague and slow even in sport mode. Jeep would do well to tighten that up a lot.

But overall, the Jeep is a hit. The cabin now has the quality to match the continuing excellence of the chassis, and the infotainment system interface is among the best. Although the driving experience still isn't class-leading, the wider package is a very worthy contender.