Hard shift automatic

i bought a 1999 forester a few months ago. First five - ten minutes of driving in the morning it has a hard shift from 1st to second. the rest of the automatic shifts are fine. I have been starting off in second and shifting up gears as needed. After say ten minutes of driving i can put shifter in drive and i don't have any problem there after. all shifts are fine. I changed transmission fluid and both filters, internal and external.I refilled with subaru transmission fluid but i still have hard shift from 1st to 2nd. Seems like the transmission fluid has to warm up before this problem goes away. Should i try synthetic and what brand??? Thank's