I've bought an auto with gearbox issues

[MyMorningHasBroken]

I part exchanged my old car about 2-3 weeks ago with a newer and more expensive one. It has 42,000 on the clock and only 1 previous owner. I had someone out to do a pre purchase check on it as i don't know much about cars myself. It was all grand!

Then I started having problems. It's auto and when I shift into D or R it can jump quite violently. This is not all the time. I can't pinpoint when it is doing it either. It does/doesn't do it when engine is cold/hot.
Anyway, this was only happening when I started up the engine to move off but today it's done it while waiting at a junction - so I didn't even shift gears. IYSWIM?

It doesn't feel right. It pulls sometimes I feel when driving but I can't really explain.

I am really worried that an auto with a gearbox issue is the start of a nightmare.
No engine lights on so ob codes are coming up which makes me suspicious that they may have been wiped permanently (is this possible?)

I have a 3 month warranty (need to read though it now) but I am worried they will try and fix it but the problems will start again after the 3 months is up.

What can I do?

Also, Do I have rights to get my money back or to exchange it and for how long?

My auto 4x4 got a bit clunky in the gear changes and I had the transmission fluid drained and replaced. Made all the difference.

Could it be something as simple as that? (If so it's a cheap fix too!)

Maybe Maintland. I'd hope so.

Would it need changing though at only 42,000 miles?

I think the new rules allow you to reject during the first 30 days so act quick! Not 100% sure on this but worth a google!

Thanks Shark. I dod google and can see why they are dragging their feet. Took in today as they said they were too busy last week and said they would ring Vauxhall to check for any updates. They haven't called me back.