Moving from Texas (no state tax) to California (state tax). If residence in Texas January but Calfornia residence Feb - Dec. Am I liable for any CA state tax for the Jan income in Texas ? Also if I decide to sell taxable stock in Texas in Jan would be this be liable for CA State tax ?
You are not liable to California on income earned while a resident of Texas as long as all that income is Texas sourced.
Once you become a California resident then California has has a claim on your "worldwide" income.
So if you perform your job in Texas (or any other state that's not California) in January, it's not California sourced. Likewise if you sell stocks in January in Texas, the capital gains are not California sourced.