Well - some transmission will do that until you drive the car enough to have it learn your particular shift strategy. Same thing happens when you let a family member drive the car for a week or two and they return it back to you. The car will drive quite differently than when you drove it previously. The transmission in the Corolla is a "learning" transmission - will take a while before it settles down.
Also check to make sure that the fluid level is OK - the 9th generation Corolla (2003+) tend to be hard on transmission fluid and fluid changes will require Toyota Type T-IV ATF. Use of any other kind will tend to alter shifting characteristics or even damage the transmission. If the car was "serviced" before you bought it - make sure if they changed the fluid, that it was teh correct type. Also, I tend to avoid transmission fluid flushes - most will do more damage than good. If you got a flush right before you picked up the car - that probably explains the odd behavior.
Good luck.
2002 Corolla S, Silverstream, 1.8L 1ZZ-FE (VVT-i)
2003 Matrix XRS, Cosmic Blue, 1.8L 2ZZ-GE (VVTL-i) - RIP
2009 Matrix XRS, Blue Streak, 2.4L 2AZ-FE (VVT-i)
