Biological process

positive regulation of gamma-delta T lymphocyte differentiation, positive regulation of gamma-delta T-cell differentiation, positive regulation of gamma-delta T-lymphocyte differentiation, up regulation of gamma-delta T cell differentiation, up-regulation of gamma-delta T cell differentiation, upregulation of gamma-delta T cell differentiation

Any process that activates or increases the frequency, rate or extent of gamma-delta T cell differentiation.

positive regulation of gamma-delta T cell development

Note that immunologists typically use the word 'development' to refer to cells of B or T cell lineages undergoing the process that GO describes as 'cell differentiation'.