Tunnels of Mount Gram is a location with the text: " X is the number of captured cards underneath Tunnels of Mount Gram. ". Does this effect stack with other copies of Tunnels of Mount Gram in play?

Nope! Here's the relevant entry from the FAQ:

(1.31) Self-referential effects
If a card refers to its own title in its text it should be
read as referring only to that copy of the card. A card
that refers to other copies of itself will use the language
“any copy of...” or “another copy of...” or “a card with
the title...”