My sister has a 2004 civic ex auto and at high speeds (45-65mph) when she tries to accelerate it seems as if the car gas trouble shifting? Im not sure. But it’s as if the car is redlining at 3.5-4k rpm. The car shakes and if you keep on the gas for a few seconds it will eventualy upshift but theres obviously a problem. Im not sure what exactly it is but if anyone could help me out i’d appreciate it

 

What has been the history of ATF maintenance? If you haven't been doing a drain and fill of Honda DW-1 ATF at least every 3rd oil change, then you are behind in this service IMO. You may need to play catch up here with a 3 times drain and fill of Honda DW-1 ATF while driving in between to refresh the ATF. No flushing is advised.
Another area of stumbling or stuttering or hesitation at highway speeds is a failing EGR valve or clogged EGR ports with carbon. Some have described the symptoms of this problem as driving over washboard type roads.

 

The trans fluid hasnt been changed in a while.. thanks for the info i’ll try that and see if it woks