before you do anything, take it out for a 10 mile run on a motorway... if it's full of soot, or the cats' blocked, a good run will clear it. then if it still judders, it's probably a fuel starvation problem. you could try disconnecting the vac hose from the egr (block the open end with a screw) and run without active egr. is air filter ok?
whats the power like?
edit: i have a feeling it might be stuck egr valve. definitely try egr deactivation- pull vac hose off.