I believe two of the problems with the Dublo 08 were overheating due to lack of ventilation (increased in later versions by removal of some metal?), and the coupling rods, which were binding if in one piece (later ‘cured’ by having two piece rods).
I don’t run my 3-rail 08 version (converted from 2-rail as it was cheaper to buy) very much, but it pulls quite well. I could not fit a 3D crew inside as there is no space, so I printed a driver on paper instead.
The worse problem with later Dublo locos was the nickel-silver wheels which did not grip as well. One of the best ‘pullers’ is the Co-Bo as this has traction tyres.