overheating

First time poster long time reader.Almost everytime you guys hit the problem on the head..I have a 1500 ram that just started to overheat when pulling my boat,the boat is a 23 foot supra weights about 3500# or less.Never had a problem till just a few weeks ago..Changed the stat and the fluded to 50/50 and flushed the core out..Just to hot out or i need a bigger core??

check trans