New Symptom!!

My 98 k1500 runs at less than a hundred degrees without thermistat. But as soon as I install a stat the truck reaches operating temp it wants to die and starts overheating shortly after the chuging an dieing systoms start. Could this be the cause of a cracked Intake? I have replaced everylast thing on the cooling system even had the heads machined every thing is new as far as cooling goes I feel like I keep running into a wall.