Complex sentence: Both stations had unusual "joint primary" affiliations with both ABC and CBS, from 1965 onwards, and although KFBC/KSTF slightly favored ABC and KOTA/KDUH slightly favored CBS, that didn't help the duplication problem.
Split into simpler sentences: Both stations had unusual "joint primary" affiliations with both ABC and CBS, from 1965 onwards. Although KFBC/KSTF slightly favored ABC and KOTA/KDUH slightly favored CBS, that didn't help the duplication problem.