In the context of equational reasoning, J. Avenhaus and D. Plaisted proposed to deal with leaf permutative equations in a uniform, specialized way. The simplicity of these equations and the useless variations that they produce are good incentives to lift theorem proving to so-called stratified terms, in order to perform deduction modulo such equations. This requires specialized algorithms for standard problems involved in automated deduction. To analyze the computational complexity of these problems, we focus on the group theoretic properties of stratified terms. NP-completeness results are given and (slightly) relieved by restrictions on leaf permutative theories, which allow the use of techniques from computational group theory.