I have a 2002 Octavia 1.9 diesel automatic and it has a problem

1: there is a judder at a certain speed, It was in it when I bought the car a year ago and I thought for a long time it was the gearbox, but I've noticed recently the judder happens in most gears but only at a certain engine rev, I have pinpointed it to around 1500rpm -1800rpm ish and once you press the accelerator down it goes so I'm now thinking its more likely an engine mount

Any ideas or suggestions as to which it is?

Has it ever had its gearbox oil changed, if not might be worth changing it,

I would check lower dogbone mount, bushs might be shot and causing vibration under load