I have received a lot of good advice here over the years and thought I would pass this on for what it is worth. I have had trouble shifting into first gear for just about as long as I owned the car. The only way to ensure good shift was to first put the car in 2nd gear (or third if that did not work). Dreading the cost of a new tranny I put off the trip to the garage. I had them look at it when I was having a new valve cover gasket installed (smell of burning oil) and they came back with two saging motor mounts. They replaced the mounts and the tranny shifts perfectly.

Hope this helps!