GOTO statement causing jitter in output frequency, can be this fixed?

[HenrikOlsson]

And since the four pins are on the same port you could do away with the individual RMW-instructions for each pin and just do

x = 0
masfrk:
  PortC = x
  x = x + 16
  pauseus 194
goto masfrk

Or even

PortC = 0
masfrk:
  PortC = PortC + 16
  pauseus 194
goto masfrk

Obviously this will cause the bottom 4 bits of PortC to be 0 but it doesn't look like you're using those for anything.