Get template part vs locate template function

First of all note that get_template_part internally uses locate_template, so your feeling that the latter is slower is wrong.

If you look at the code, get_template_part is little more than a wrapper for locate_template, so if one work and the other not, there are 2 possibilities:

• you are using get_template_part wrong
• there’s some hook on "get_template_part_{$slug}" action that prevent it works

However, if locate_template works, use it: it’s not slower, to be honest it can be pretty faster if there are functions hooked on "get_template_part_{$slug}" that slow down execution.