I would just do the flush and see how it runs afterward.

 

I would try doing the flush, it is an electronically controlled transmission so you could try disconnecting the battery to reset the shift perimeters. I would also clean the throttle body while the battery is disconnected then reconnect it and drive it around and see if anything changes. 2500 seems to be a normal shift point for 1st to 2nd. I've noticed that on my car since the repair that my engine mounts took a beating from the old transmission jerking so hard and slipping that now my transmission feels like its shifting hard but its actually the engine mounts that I'm feeling.