Multiple degenerate band engineering has been established as an effective approach to maximize electrical transport in thermoelectric materials. A series of polycrystalline samples of chalcopyrite Cu1-x-delta AgxInTe2 (x = 0-0.5, delta = 0.02-0.05) was synthesized, to achieve multiple degenerate bands. A pseudocubic structure is realized when x is around 0.2. As a result, the degenerate valence bands influence electrical transport significantly. In addition, the lattice thermal conductivity is significantly depressed in the solid solution due to the strong phonon scattering by strain-field fluctuations, since Ag substitution brings significant anharmonicity to the crystal structure. The highest ZT of 1.24 was obtained at the composition Cu0.75Ag0.2InTe2. This study provides an example how the pseudocubic crystal structure is applied to design and evaluate the TE properties in diamond-like compounds.