DUAL PATH Transmission shifting late

[DomC56]

Hi,

I have a 62 Skylark with a Dual Path transmission, I've owned the car for a little over twenty years. For the last four years it's been just sitting in the garage. I took it out and started to clean it up because I got laid off from work and I have to sell it. After changing the engine oil and putting in a new battery I took it for a ride. The transmission used to shift from low to drive around 10mph, now it's not shifting until 45mph. I'm going to order a pan gasket and filter and try changing the tranny fluid to see it that helps. Anyone know anything else I can check or do to get it shifting right again? I'm hoping it doesn't need a rebuild, I really can't afford it right now.

Thanks for any help.

Dom