00 Grand Am SE Shifts hard

My 00 Grand Am SE 4- cylinder, has 78,500 miles on it. The only problem is that sometimes when I take off, it shifts really hard from 1st to 2nd, but that is the only gear that does it. Does anyone know what could be wrong?

I had that happen on my GAGT. End result. I replace an ECU, Differential, and a transmission in the same day.