Modifying Hitboxes on Player Models?

I am part of a Gmod TTT server that is unable to use quadruped models because the hit boxes don’t work as well as biped models. How would I go about fixing them and what programs can I use to modify/fix them?

I’d suggest you use this tool to check how the hitboxes actually look on your quadruped models and see if they’re the same as a biped model, or fitting. The hitbox is defined by the model’s author, and if they’re not doing that, then it’s not a quality model. To my knowledge, there’s no easy way to actually modify it within Garry’s Mod. You could always try to recompile the model with a fixed hitbox, but I don’t know if that’s possible since I don’t work with models.

Well from what I’m told TTT has specific heights for hitmarkers or w/e. There’s no way to fix it so they work properly? Or is it not the hitboxes, and if not, what could I edit in the server?

If the hitboxes are normal (as in, correct for the playermodel), then it’s a problem with TTT and would require a modification of it. That being said, I’m not sure what you would need to modify if TTT is the issue.