As a noun, in the US and Canada, lumber refers to sawn logs or ready-to-use timber.
In contrast, in the UK, lumber, as a noun, refers to useless, irrelevant household articles that are stored somewhere out of sight. Imagine this.. One of those deserted manor homes with lumber in each cupboard of every room!
As a verb the word sustains its various geographical interpretations.
In the US and Canada, the verb ‘to lumber’ is associated with one working in the wood and timber industry – the ‘lumbering’ industry. A ‘lumberjack’ is someone who earns his living in wood and timber industries.
In the UK, the meaning of the verb ‘lumber’, implies that someone is encumbered with unwanted goods and materials or has had the same foisted upon them unwillingly. It is also used to indicate that one is burdened with a tiresome, tedious task or situation.
In Australia, the meaning is specific: it means to arrest or imprison and, not surprisingly, this usage arises in the 17 Century.
Cutting across all these conventions is the verb that describes a particularly awkward walk. When someone ‘lumbers along’ they are certainly struggling to walk and are likely to be physically encumbered while doing so. In this context, the verb can be applied to a living or mechanical modes of transport. Thus elephants, used as beasts of burden, would lumber along forest tracks in Thailand as much as a heavily laden goods train would lumber along its track, making a deafening noise as it did so.
I would encourage you to use this word as one of those that provides texture and mental pictures to your listeners. Placed in accurate context, it could serve well as a punch line or as an essential component of a narrative.