Terios Gearbox chug/dragging


My mum has a 2002 Terios. Had some gearbox issue's with loud whining and leaking alot of oil.
Before this began the mechanic told her on it's the last service it needed the gearebox replaced. Her mistake for not getting onto it sooner.

However! Now that the gearbox is replaced it feels like its stuck in 4WD.
Doing a U-turn causes the car to chug or jump as if it's about to stall, so you give it some more revs but the whole thing feels like there is resistance and drag. The gearbox feels sticky and a bit clunky, getting into gears (especially reverse) is difficult at times.

We will be taking it back to the mechanic but im concerned he might be having her on a bit.

Any info anyone can give, or thier opinion on what this might be, or if there is a mistake the mechanic could have made to cause this. Would be much apppreciated.
I have some mechanical knowledge and have worked on cars a few times.