Raylo

Not sure about your exact 4.3 version but some later ones at least had 2 engine temp sensors, 1 for the gage and another for the computer. Like Octaneman said the computer engine temp sensor could be sending a way off signal that could change the fuel to an inappropriate mixture for the ambient conditions and possibly prevent closed loop status. The 4.3s I have worked with have gage sensor on drivers side block and computer sensor near the t-stat housing. Man, with all that has been done to that motor it should hum. Good luck, I hope you get it.