General synonyms:
* Trudge
* Tramp
* Hike
* Walk slowly
* Amble (implies a leisurely pace, but can also be used for slow and tiring movement)
* Stroll (implies a leisurely pace, but can also be used for slow and tiring movement)
* Wander (implies a lack of direction)
* Lumber (implies heaviness or clumsiness)
* Shuffle (implies a slow and tired walk)
Words emphasizing effort:
* Toil
* Labor
* Struggle
* Slog
Words emphasizing slowness:
* Creep
* Crawl
* Drag
* Dawdle
Words emphasizing monotony:
* Drone
* Grind
* Mope
The best synonym will depend on the specific context and the nuance you want to convey.