My girlfriend is having car problem with her 97 Dodge Stratus drive down the hwy & then the...?

Sounds like it could be inappropriatly shifting down gears. (This would explain the sudden jerk and jump in RPMs, as the engine would have to rapidly increase RPMs to make up for the new gear ratio at that speed, causing a jerk.) Something is possibly wrong with whatever decides when to shift gears. (i.e. transmission control; I am uming it is an automatic.) The check engine codes also seem to point to a problem in that area. (IE transmission control and the shift solenoid I beleive is also related.)