[cooperhw]

Sounds to me like you might still have an air pocket in the back.
Best way I found to get "ALL" the air out is to remove the radiatior cap, open the overflow bottle lid, and take the steam port line off at the engine. Then jack the vehicle as high up in the air as possible so that the top the rad. cap is much higher than the rear of the motor. Fill all up and let it sit. about every 15 minutes add any water that it needs to keep it full. What this will do is allow the water near the top of the rad. to migrate into the back of the LS motor steam passages and it will displace (push) any trapped air towards the front and out the steam passage at the front of the motor. As soon as you see solid water coming out of the front steam passage you are done, put that line back on and lower the vehicle. Usually takes me about 30 minutes, and works every time.
If it's still going past 230 you have another problem, but 220 is fine with these motors. They like to run 220+ when AC is on.