My 97 Taurus shifts hard going into 2nd gear only. It started as just a cold problem but now does it all the time and there are no computer codes stored.
You should check your owners manual for the maintenance schedule. Is a transmission fluid change on the schedule and if so, has it been done according to the schedule?
Next, look at the transmission dipstick. What color is the fluid? If it is red, then it is good. If it is brown, reddish brown or (worse) black, then get it and the filter changes ASAP. I would recommend against a flush, but if you decide to do that, make sure they drop and clean the pan and put in a new filter before doing the flush, otherwise they could damage your transmission.
You should take this to a trans shop and let them check the line pressure on it. Its possible that one of the accumulators is leaking on it causing the harsh shift. A trans shop can narrow down the problem for you.