The Two Worlds of Jennie Logan(1979)
Shortly after moving into a new house with her philandering husband Michael (Alan Feinstein), Jenny Logan (Lindsay Wagner) finds an antique dress in the attic. After putting it on, Jennie finds herself flashing back 80 years in the past, where she falls in love with handsome painter David Reynolds (Marc Singer). Soon she finds herself bouncing back and forth between the two realities, and becomes obsessed with solving an 80 year old murder.
Although many seem to associate this with the Christopher Reeve film "Somewhere in Time," this premiered on television first, and was based on the novel "Second Sight" by David Williams. The film was released on video, but has been out of print for many years.