urgent p38 dse help, gearbox?

hi people, im in need of some help. My dse hasnt run properly since i bought it a coup'e of months back. The main problem is lack of power. I have replaced the in tank fuel pump which wasnt working, no change. Replaced burnt out starter motor and fitted hot start fix, no change. When driving along now the car has started to accelerate on its own and then cut out with the management light on. It takes a lot of ignition on and offs yo vlear the light. Whilst the light is on it will not start. Now when it cuts out it says gearbox fault on dash and is now dangerous to drive as it keeps accelerating on its own. Initially the problem did seem like fuel starvation when i needed power but now it is overfuelling alot. What are peoples thoughts? I need to get home 70 miles on sunday. Map sensor? Gearbox? A ll hoses seem ok