Outrageous tax appraisals! Advice needed

[Joseph Weisenbloom]

I just got my property tax notices and my jaw nearly hit the floor. I invest in Texas which is a non-disclosure state which means to the best of my knowledge the appraisal district is not discolsed the sale price. I noticed an interesting trend within my tax bills. For the properties I bought last year my taxes spiked 50% from the previous year. For the properties I have had for a few years there was no major spike in the taxes. 

Is it just me or do they look for the properties that just had a deed transfer recently and focus on those for tax hikes? I made zero improvements on any of these properties yet I am getting hit with a massive increase. I am obviously protesting these appraisals. Any advice?