So when i'm at speed and if i get on the gas like I wanna pass someone my car shutters(hesitates) and feels like it upshifts funny doesnt stop till i let off gas somewhat. But when im at a stop and accelerate it is fine.. Could it be a tranny problem? I'm hoping i can fix it somewhat. If anyone has any idea it would be appriciated. Thank you

91 cuttlas ciera 3.3

Does anyone have a idea why it would hesitate when i accelerate at speed and not from a stop? I drive it daily to school and back but it is so annoying i can never speed up after in in 2nd gear(30mph+) It jerks a bunch until i let off the gas especially around 50 mph...It starts fine and idles fine... I need help!!:banghead: