After a day of testing I might finally have found the issue
I drove on the motorway and started testing driving in manual. I shifted down to 3rd and accelerated hard. If I put the foot all the way to the bottom the car would max out at around 4500 revs. If I let go slightly, just before that tick point it would accelerate slower up to 6000 etc. That happened in 2 and 3 - gears I tested. I assume this sounds like a fuel pump issue - is my assumption correct?