I have a 51 plate D22 double cab. It is the TD25 nissan engine, it is a bit of a snail compared to later models, but then it doesn't throw a con rod like the later YD25 engine (which is actually a Renault lump :roll: )
I get about 27mpg as an average. Has dropped to 23 if towing a loaded car trailer, but with care can get nearly 30.
Mine has done about 130k miles now and has only needed normal maintenance (which has included set of tyres, front brake pads and a couple of lower ball joint on the front suspension)
HTH