94 2.2 litre transmission problems

I have a 94 cavalier with a 2.2 litre engine.
My porblem is that when i maintain a speed of about 58 km/h, the car begins to jerk, not violently.. but noticebly. It also happens at around 70-73 km/h.

These aree the only speeds i have found that it occurs at, so i am wondering what the problem is if there is one.. and how i would go about fixing it.

any help would be greatly appreciated.

Thanks in advance.