Amazing overheating problem...desperate

This symptom caught my eye:
"-YES, pushes water out of overflow tank then bunches of hot hot steam"

This is quite abnormal, and indicates possibly that:
- The system is not getting anywhere near all the air out at filling (despite the hole in the t'stat). The coolant in the engine is flashing into steam in short order, and once the t-stat opens, just pressurized steam is coming out of the engine and pushes through the water in the overflow tank. The pressure would have to be somewhat high to do this, which indicates hard boiling in the block or heads. And I can't tell you how well or poorly the rad cap will seal in the presence of just steam rather than hot coolant.

Can I suggest that you go through the burping process slowly and repeatedly and with just 1-2 minutes of run time at any time, then allow a cooldown and repeat? Also, make sure the truck is pointed up hill; put it on a jack if you need to.

Another suggestion- Put a pressure gauge cap on the rad and stop every minute to see what is going on.

Questions:
- Does it do this if you start cold and idle, and not drive?
- What radiator? Does the cap actually match the rad opening for 100%
- What coolant is being used?
- Heater core hooked up? Do you open that when you burp the air out?
- Engine mounting normal? Not sloped 'downhill'?
- Any pix of the installation that you can share?
- Cooling fan(s) set up?
- Any excess water in the exhaust? Indicating that coolant is leaking out an exhaust port overnight?