Thank you for your question and I understand your concern.
If the new drain pump is not running and there are no loose wire connections in the drain pump circuit, the control board is most likely faulty.
I would check voltage output to drain pump when it’s energized. If no voltage, replace faulty control module.
NOTE: I do not recommend measuring the voltage supply at the drain pump unless you have experience and feel safe and confident in doing so; otherwise I recommend calling a service technician to diagnose and repair your washer.
The #88 is not a code and it is not listed anywhere in the service manual. When you enter the test program and advance to the drain pump test, P15 should display and Start/Pause should be flashing. It also does not make reference to error or #63 when you pulled the pressure switch hose off.
Since you replaced the drain pump, the control module is most likely faulty if the drain pump is not getting the voltage supply.
I hope this is helpful. If I may be of further assistance as more details become available, please reply to this post along with the model number of the washer.
If you get to the point where you need to have a service technician diagnose and repair this failure, you can schedule service through this link:
Sears Home Services.