Got Transmission serviced by flushing system. Shift problems occurred while at dead stop to first and then later all gears would shift hard. No mechanic could figure out why and no codes came up. Took in it several times with no results. Took car on 2500 mile trip after getting it checked out and okayed by reputable mechanic. Transmission started acting up worse and then had display panel problems. Returned from trip, codes finally showed transmission problems. Had new GM transmission put in, New display panel, PCM Control cluster, and now ignition switch replaced. Stupid car is still having problems shifting into 1st from dead stop every now and then and also will shift hard on occasion. Seems I spent $4000.00 getting all this done for nothing as it is now continuing with exact same very intermittent problem that I had at the beginning. No codes at all are showing up and nobody knows what to do! Could it be as simple as a vacuum problem that the Quick-Lube guys messed up way back when they flushed the transmission or what? Help…as I do not wish to go thru all of this again!!!
Harsh shifting is sometimes caused by a faulty pressure solenoid in the tranny.
Problem here is, you have a NEW OEM tranny in.
Another thing that can cause sift problems is a a faulty VSS (Vehicle Speed Sensor).
Perhaps Transman18 can help if he comes around.