In Classical Nahuatl, non-possessed nouns would take the absolutive case with -tl for nouns ending in vowels, and -tli for nouns ending in consonants. [0] Here, as you mentioned, <tl> marks a single consonant: the voiceless alveolar lateral affricate /tɬ/ [1].

[0] https://en.wikipedia.org/wiki/Classical_Nahuatl_grammar#Noun...

[1] https://en.wikipedia.org/wiki/Voiceless_alveolar_lateral_aff...