Concern with torque

[Surf01]

We are concerned about towing with the Surf as it seems to struggle up some hills. No issues on motorway even with long hill on M5 south of Bristol.
At times the speed drops down to about 10-15mph when towing 1800kgs. Surf 3rd gen 3.0L auto is rated to tow up to 2200kgs so not sure why it should struggle with 1800kg. Fish Hill and Birdlip hill are good examples. By the time we get to the top we are really crawling. No over heating issues.
With my previous Surf also a 3rd Gen but a 1997, I had no issues so I suspect that for some reason there may be an issue with the torque or changing of gears. Seems to stay in 3rd and even manually changing down to 2nd or 1st makes no difference, but then it may be in 1st already. Transmission fluid changed about 2,000 miles ago on service.
Can any one advise if perhaps the ECU needs checking etc to improve towing capabilities? Otherwise no issues.

[Surf01]

Is it possible that the auto gearbox is staying in third and not changing down and the truck then running out of steam?

[Wolfracer]

is birdlip just past the air ballon island or the bit before it ( coming from the north)

They are both feckin big hills, and would expect most towing vehicles to struglle with a big load on....

[Surf01]

The bit before it. You leave M5 south of Gloucester turn off going towards Swindon (A417?)

[Wolfracer]

The bit before it. You leave M5 south of Gloucester turn off going towards Swindon (A417?)

Ah ok..that's an extreme and extremely long gradient. I'd err on the side of caution going up there and not "push" it too hard anyway.
On the other hand I used to work at Woolworths DC in Swindon and did the commute everyday in a 2.0 turbo Astra coupe... it didn't struggle.

[Surf01]

Ah ok..that's an extreme and extremely long gradient. I'd err on the side of caution going up there and not "push" it too hard anyway.
On the other hand I used to work at Woolworths DC in Swindon and did the commute everyday in a 2.0 turbo Astra coupe... it didn't struggle.

LOL!