Can you post a pic of what you're dealing with? I can't imagine there being an issue with shearing the plug off the sensor if you use the right wrench but maybe your setup is a little whacked or something.

 

I was only able to find this one picture of the heater core supply tubes, item #79 on this diagram:



Further inspection of the diagram indicates an ECT sensor as item #80
My heater core supply tubes dont have this sensor, just a dummy plug... maybe its time for a little cross referencing?

Checked around, seems like the two sensors from the 96' explorer and the 88' F150 should have the same threads. When I get to the parts house ill need to pull both of them to double check, should be pretty seamless swapping the two.

 

If that is the case I can see this being hard to get at, looks like you may have to remove the distributor at the very least and if you still can't get the plug out remove the upper intake and take that whole tube assembly off to have the plug drilled out.

P.S. There has to be a coolant temp sensor somewhere on this motor, are you sure there isn't one elsewhere in the intake or in some exterior tubing?

 

I was thinking, if that piece doesnt want to budge, then maybe ill put a threaded brass tee fitting on the hose that goes down to the water pump, and have the fittings for the hose barbed, while the one on the middle of the tee can be for the sensor. Any thoughts?

EDIT:
It should be where this plug is! But all I see is a plug. I went over the engine and couldnt find any other spots..

EDIT 2:
75 373675 Water Hose Connection Bolt
76 8255 Water Hose Connection Gasket
77 387822 Lower Intake Manifold Stud Bolt
78 9439 Intake Manifold Gasket
79 9D424 Intake Manifold Heater Inlet Tube
80 12A648 Engine Coolant Temperature Sensor
81 373724-S101 Coolant Hose Fitting
82 87617 Port Plug (2 Req'd)

 

I'm sorry but I don't have any tips for you. I've only ever messed with my Mustangs intake set up and Mustangs are easy to get to the ECT's, I have no clue how the Explorers are set up.

 

So I officially can be declared an airhead.

Was talking to a church friend outside of church just a few minutes ago, hood was up, and I was checking around, and something told me to check the vacuum lines all over as per Puddys comment, lo and behold the fuel regulator vacuum wasnt even connect at the regulator.

Still need to plumb in the sensor, bought a new one today as well as some fittings to get that issue resolved, but WOW what a difference one vacuum line can make.

 

Glad you got it!

 

One small issue is it still wants to kind of stall upon shifting right after startup, could a vacuum leak do that?