Suzuki Grand Vitara 2/0 TD XL-7 - Accelerating problem - pmax

I am hoping that someone could give me some guidance, I have noticed that when I try to acclerate, when the car gets to 3000 rpm, it starts to struggle to get past 3000 rpm, it is as though the car is not getting enough fuel.

Sometimes, when I try to put my foot down on the accelarator pedal there is what I would describe as a dead spot, when I release it slightly it starts to accelerate again.

I went to try another XL-7 which was slightly older and had more miles on the clock but it seemed to have a lot more power than mine and had no difficulties in getting past 3000 rpm.

My father in law tried both cars and agreed that mine seemed to have less power than the one I went to look at.

Has anyone else had the same problem or give me any ideas of where I should look.

Someone said that cars can behave differently depending on how they have been driven but is that true with having dead spots when pushing the accelerator pedal down?

I look forward to hearing from you.