Need help with overheating 454 Firetruck

[ARTEMIS1759]

It is puking coolant but never thought about exhaust.

 

[Mike Napolitano]

I would check the hoses like like wingman but also check for proper air flow through radiator, even though it was replaced if the truck has an A/C condenser or auxiliary transmission coolers their air passages may be block and sometimes aftermarket thermostats are defective, I have gotten burned a few times. Also you said you replaced the engine, is it a GM remanufactured or an aftermarket rebuild. And did the problem start when engine was replaced or before