Do firmware updates affect print speeds?
I agree with @silver, but also wanted to point out that maybe the acceleration values on the old firmware you had were different from the default in TH3D R2.7.

The current settings can be retrieved using the M503 command, which should return the values from the eeprom:

Maximum Acceleration (units/s2):
M201 X1000 Y1000 Z100 E10000
Acceleration (units/s2): P R T
M204 P400.00 R1000.00 T1000.00


You can then lookup the default settings for your printer model and use M201 and M204 to set the new values. Then M500 to save the new settings to the EEPROM.