Gearbox not changing up

[Bongoplotter]

1997 Diesel, closing in on 300k miles and really hope this won't be the end!
Gearbox working well until the engine warms up and then not changing up until almost 300k revs at times, then when it does change, it's with a real jerk. Topped up the gearbox oil which seemed to help for a few days but there's something else going on. Sensor maybe?
Already spent £700 with a Bongo "Specialist" who was specifically asked to check the sensor but did anything but. Not going there again!
Any advice welcomed, thanks.

[g8dhe]

Nothing as simple as the Throttle Position sensor TPS ? Has any work been carried out previously, might not have been done up tight enough and has moved ? Its the device under the drivers seat with 466 labelled across the top.

[Northern Bongolow]

What work did you have done?. Engine speed sensor at the front of the engine (crank sensor). May just need removing and cleaning, they can get oil on the sensor face and start acting up, or the wire needs checking, it's an easy check.

[Bongoplotter]

The guy was asked to fix an engine oil leak and investigate the gearbox problem. He changed the gearbox fluid, changed the brake fluid, added inhibitor for the engine oil and changed the glow plugs.

[Northern Bongolow]

Check the vac pipes are all in good nick, (not split ) or left off, and the little green filter on the turbo pipe connection, these can get disturbed when doing the glow plugs.

[Bongoplotter]

Thanks Geoff & Northern Bongolow
TPS sensor is now replaced and the mechanic wondered why there are two screws where you wouldn't expect there to be!

image0 (2).jpeg (22.16 KiB) Viewed 7328 times

image1 (2).jpeg (21.6 KiB) Viewed 7328 times