2015 Vauxhall Zafira vauxhall zafira tourer acceleration issues

Hi, I posted a few days ago to ask about my car and repairs on clutch.

Took the advice and shopped about to find a cheaper quote not by lots but enough to make it an option now.

My issue is this, the car has stopped playing up and a highly recommended garage when I asked on a local group.

Took the car for a run, and has said nothing wrong with the clutch at all, car would not repeat what has been doing for me.
Have said they will replace it but don't feel the clutch is an issue.

But when I describe what it's doing they have said it could well be gear box itself.

Driving home today I needed to join motorway driving up the hill on slip road.

First second third fourth fine accelerated absolutely perfect, I put the car in fifth revs shot over to 6000rpm, on the gear change indicator, it's stating up 3, I'm in fifth, I chucked the car in 6th, revved even more and then stated up 2,
Put the car into 3rd then 4th calmed down into 5th and 6th.

Any idea I know iwas in 5th not 1st or 2nd.

I'm at a loss at the moment.

No way I have the funds to get the clutch and dual mass flywheel done for it too come back ok and then it's gearbox.

It's not on finance and my partner has said just get rid never been over the moon with it the drive and fuel economy have not been as good as expecting.