I had idleing issues with my 94 gt convertible when I first got it to, it was my harmonic balancer. My transmission is automatic and it went shortly after buying it
. Anyway my transmission did not jerk at certain speeds it just one day started slipping and just gave out one day. I had it rebuilt with a Fairbanks shift kit and crown Vick interceptor valve body part idk. Anyway if it needs to be rebuilt get a Tranny cooler they save the life of the transmission. I hope yours doesn't need to be rebuilt but I'm sorry I can't help.