Vauxhall Insignia judder when in 5th and 6th gear above 60mph

My insignia had it's first service at 22k and a week or so ago code 82 - oil change and code 55 - DPF change came on. I do alot of motorway driving so never thought anything of it and thought I'll book it in asap as the service isn't due. However last week it started to judder over 60mph and i have to shift back to 4th gear. It's fine on local roads up to 40pmh but as soon as it goes onto the motorway it's not happy. It's now at 33k and Vauxhall said it needs a full service at a cost of £300 without looking at it and said he would quote for a new DPF. Is this not under warranty? I'm a bit confused about that and can I run it in and find out what's wrong without them fixing it? Also is the diesel particle filter and the particulate filter one in the same? Help please! Jac