Involved in the biosynthesis of L-digitoxose, an unusual dideoxysugar attached to various pharmacologically active natural products, including the antitumor antibiotic tetrocarcin A, and the antibiotics kijanimicin and jadomycin B. Catalyzes the reduction of the C-3 keto moiety of dTDP-3,4-diketo-2,6-dideoxy-alpha-D-glucose to yield dTDP-4-keto-2,6-dideoxy-alpha-D-glucose. Also able to reduce dTDP-3-keto-6-deoxy-D-galactose and dTDP-3-keto-6-deoxy-D-glucose to yield dTDP-fucose and dTDP-quinovose, respectively. dTDP-4-dehydro-2,6-dideoxy-alpha-D-glucose + NADP(+) = dTDP-3,4-didehydro-2,6-dideoxy-alpha-D-glucose + H(+) + NADPH kcat is 6.24 sec(-1) for dTDP-glucose as substrate. Antibiotic biosynthesis. Homotetramer; dimer of dimers. Belongs to the Gfo/Idh/MocA family.