02 Chevy Trailblazer, running too hot about 235° before I let it go any further... I had antifreeze boiling back out the reservoir over flow, so i replaced the thermostat (with a good ac Delco brand thermostat) still over heating... what should be my next step?

 

Have the cooling system cleaned. A good back flush could help. Are there any leaks? Is the water pump working well?

 

when does it overheat? idling? driving? right away or does it take time?