Start with a silverback gorilla, make it roughly three times bigger, assume its bone and muscle structure is capable of compensating for the increased size: how fast can a thing like that reasonably move, when it's not sprinting but it definitely has somewhere to be? Would it be faster or slower than a human moving on foot at the same level of urgency, and is that linear or does it depend on the speed?
Gorillas weigh around 350 pounds (around 150 kg). If your giant gorilla has three times the mass and the same proportions, it would be around 1.4 (cube root of 3) times taller, standing at around seven feet tall. A very large gorilla was once shot that weighed over 600 pounds (270 kg) and was just over 6 feet tall, so a 1000 pound gorilla is not such a huge stretch.
Gorillas can usually run at 25 mph (40kph). Larger species of similar animals tend to move faster, e.g. the African Elephant is faster than the smaller Indian Elephant. If your giant gorilla is part of a species of gorilla that is larger than normal gorillas, it will probably move a little bit faster, perhaps around 30 or 35 mph (60kph). If it is simply an unusually large ordinary gorilla (like the Hafþór Júlíus Björnsson of the apes), it would probably move at an ordinary gorilla rate.
If your apes gigantism is caused by a mutation or endocrine abnormality, some effects of those mutations might make it harder for it to run effectively. Humans with gigantism often experience health problems with the heart and skeleton. An endocrine problem could also be used as a reasonable explanation for a difference in behavior from ordinary gorillas.
A gorilla that is three times bigger in every direction would weigh 27 times as much (three cubed), or 9450 pounds (4300 kg), similar to an elephant. However, this gorilla could not exist in the real world. What you change about your world to make it possible will determine how fast it moves.
Here is an excellent educational video about scaling up the size of animals, if you want to look more deeply into the consequences.
Relative to human speed, any gorilla would probably be much faster, since ordinary gorillas can run faster than Usain Bolt sprinting.
3 times bigger than a gorilla is quite big, too big to fast but big enough that it needs less steps to reach the same speed.
Looking back in history some members of the ornithopoda were decently big, some way bigger than 3 times a gorilla and they walked on their front fingers which made them really slow, but they could gallop at high speeds when standing on only the back feet.
You need to understand that knuckle walking is just an evolutionary step between quadrupled animals and bipedal ism.
In the case of ornithopoda those dinosaurs where slowly transitioning from bipeds to quadrupeds, the opposite of gorillas.
So I guess a giant gorilla would adapt a new style of movement and would be really slow both when walking upright or on knuckles due to its sheer weight.