That's superb, and really appreciated.
Gearbox has started to play up this afternoon, it's holding first gear or if you put it into reverse there's a double 'thump' and the car seems like it's starting in 3rd, from drive to reverse there's the double 'thump' again
Are the sport/snow mode lights flashing on the dashboard ? Can you get it onto a Lexia and check for any fault codes ?
It sounds like its dropping into hydraulic emergency mode - in drive you will get only 3rd gear with the torque converter clutch always unlocked so it will feel even more gutless than snow mode.
Emergency mode also puts the rail pressure up to maximum pressure (to prevent clutch slip when the ECU is not regulating the pressure) which means it will bang/jolt when you go from neutral to drive and especially from neutral to reverse where it will almost make the car shake.
If its in emergency mode the snow and sport lights should be flashing, unless they've been tampered with...
Sorry if you've said already earlier in the thread, but what's the mileage and have you done any gearbox oil changes ?
Until you can get it on a Lexia we can only guess as to the exact cause though because a lot of potential faults could drop it into emergency mode from major to minor, even something as minor as no power to the ECU would do it, and oddly the fuse that supplies the gearbox ECU is in the passenger footwell fuse box!
PS when you say holding first gear do you mean holding 1st to about 3500 rpm for the first couple of minutes after a dead cold start in the morning ? If so that's normal (but annoying) behaviour....the other things you describe are not normal though of course.