Four track lack of power

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Hi Guys can anyone give me an idea of how to sort out the following issue. I have just taken possession of a four track rugger. The car drove home fine when cold 60mph easy. However when it got to temperature it would not rev any higher than 2100 rpm 50 mph max. It is the same in any gear at any speed then it struggles to go any faster. I have a 42 year old diesel land rover so I am no stranger to fuel starvation issues. The engine revs up and pulls fine to 2100 it doesn't feel like fuel starvation issue. I suspect the previous owner had the same issue as there is a new fuel filter fitted. My guess is there is a split in pipe somewhere vacuum or otherwise. Any ideas of where to look?
Thanks