digitalPin giving lower voltage than Vcc
You should connect the AVCC pin to VCC. From the datasheet (emphasis
mine):


  AVCC is the supply voltage pin for the A/D converter and
  a selection of I/O pins. This pin should be externally connected to
  VCC even if the ADC is not used. [...]
  
  The following pins receive their supply voltage from AVCC:
  PC7, PC[5:0] and (in 32-lead pack- ages) PA[1:0]. All other I/O
  pins take their supply voltage from VCC.