86 Accord LXi automatic transmission help please?

I bought this car a few weeks ago for $50.00 because the owner said it would not shift out of first gear, other than that the car was near perfect(150000 miles) so I bought it before even driving it. When I took off for the first time I drove 2 blocks and it didn't shift once. On the third block I had to cross some pretty bumpy railroad tracks and drive a fairly steep hill, After I hit the tracks the car shifted into 2nd and so on the rest of the way home. I let it sit for a few days until I got a new battery(old one was shot) and drove it for about a half hour around town and it had no problem shifting at all. Does anyone here know what this could mean? Thanks.

It is possible that the sudden jar to the car going over the bumps may have unstuck the shift shaft inside the tranny. There are no filters in those tranny's so to clean the fluid you change it every 15,000 miles. I'd change it now while it's working and it may continue to do so.