I would have put the selector in 1st and shifted it manually and keep the revs around 1500-2000, basically stopping it wanting to jump into the high gears for fuel economy. Won't be good for fuel economy but at least the gearbox isn't gonna blow itself up and I can finish the run and limp back to the depot.
for me the differential of this bus [drive shaft] is with a very long ratio so it loses a lot of grip of weight x engine power. hence the gearbox 'doesn't feel' that it has to continue forward [it seems that the engine has stopped accelerating in a straight line]. it has to be a gear ratio on the drive shaft of 8x41 or 9x39 without going beyond that [the differential].
Thankfully the engine seems to be in very good condition, it was a little rough on idle but as soon as she had a good run out and was up to temperature it settled right down and was smooth as silk. The gearbox will either need reconditioning or exchanged :)
It looks like a Voith 4-speed automatic Those also shift meaningless between the gears when the load is undefined as occurs at an incline I think this ZF gearbox is really faulty Because this hardly ever happens Chances are you will suddenly get stuck and then you really have a challenge......
