97 AWD AUTO TRANS hard swift into 2nd

About three weeks ago, the transmission started started shifting very hard into second gear. If i lighten up on the gas right at the time of shift i am able to ease the rough shift. Now the transmission seems to have what i would describe as a chattering shift. This chattering shift only happens at highway speeds at both up and down shifts.
The books i have researched don't give any info on automatic transmissions; other than to take it to a transmission shop. Which i will do, but first i would like to have some idea of what the problem is.