Hello. I have a 2000 Ford ranger automatic 4 cylinder and when i put it in drive and start to accelerate slowly my truck will kind of jerk back than go into the next gear. it only does it on that first gear shift. can anyone tell me what is causing this? or what it is. is my transmission going out? i just need help so i can get it fixed before something really bad happens

again when i put the truck into drive and start to accelerate my truck will jerk really hard while it switches to the next gear on the first gear change.

thanks for any help.