how many miles do you have?
did you clear the code after changing the solenoids?
you might want to download service manuals if you do not have one.
http://gmtnation.com/f23/need-service-manuals-get-them-here-371/
I found the following info on a different site (reference is a 5.7l, but the code logic should be similar)
Conditions for Setting the DTC
DTC P0756 sets if the following conditions occur:
Condition 1
The PCM commands first gear for 2 seconds.
The estimated gear ratio is 0 to 1.4.
The TCC slip speed is -3000 to 200 RPM.
All conditions are met for 1 second.
Condition 2
The PCM commands second gear for 1 second.
The estimated gear ratio is 0.9 to 1.2.
The torque converter efficiency is greater than 0.5.
All conditions are met for 2 seconds.
Action Taken When the DTC Sets
The PCM illuminates the malfunction indicator lamp (MIL).
The PCM commands 3rd gear only.
The PCM commands maximum line pressure.
The PCM inhibits TCC engagement.
The PCM inhibits fourth gear if the transmission is in hot mode.
The PCM freezes shift adapts from being updated.
The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
The PCM stores DTC P0756 in PCM history.
Conditions for Clearing the MIL/DTC
The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
A scan tool can clear the MIL/DTC.
The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM.