1996 gmc temperature gauge running high and no heat

The links lead me to believe there are interchangeable. In fact this page confirms the compatible models

https://shiftritetransmissions.com/shop/4l60e_98-05_4x4/

1998-1999 Chevrolet Silverado K1500 4.3L 4X4
1998-1999 Chevrolet Silverado K1500 5.0L 4X4
1998-1999 Chevrolet Silverado K1500 5.7L 4X4
1998-1999 GMC Sierra K1500 4.3L 4X4
1998-1999 GMC Sierra K1500 5.0L 4X4
1998-1999 GMC Sierra K1500 5.7L 4X4
1998-2000 Chevrolet Tahoe 1500 5.7L 4X4
1998-2000 GMC Yukon K1500 5.7L 4X4
1998-1999 Chevrolet Suburban K1500 5.7L 4X4
1998-1999 GMC Suburban K1500 5.7L 4X4
1999-2000 Cadillac Escalade 5.7L 4X4
1999-2000 GMC Yukon Denali 5.7L 4X4
1998-2005 GMC Safari 4.3L 4X4
1996-2005 Chevrolet Astro 4.3L 4X4
1996-2005 Chevrolet Blazer 4.3L 4X4
1996-2001 GMC Jimmy 4.3L 4X4
1996-2001 Oldsmobile Bravada 4.3L 4X4
1998-2001 GMC Envoy 4.3L 4X4
1996-2004 Chevrolet S10 4.3L 4X4
1996-2005 GMC Sonoma 4.3L 4X4

https://www.google.com/search?q=1999+K1500+push+button+transmission+4WD

https://www.google.com/search?q=1999+Chevy+Tahoe+push+button+4WD+transmission+4L60E



1999 - 2006

Change your motor fan and change your temperature sensor.

probably a faulty temperature sender unit
temp sensor unit which controls the fan)

Pull off the negative battery cable and unplug the sensor. See if the gauge needle returns to normal. Try tapping on the cluster to unstick the needle. No luck? Replace the temperature gauge.

sounds like low freon even though your gauges read different. i would try a can of freon and also check for alot of play in the front clutch on compressor just vibration on vehicle movement can cause the clutch pack to work.

Look for a loose connection to the temperature sender unit on the motor.
If all connections OK, you may need a new temp sender unit.

Check your cooling fans to insure they are working to cool the radiator...

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_a3369546f8067589

Try checking the antifreeze level

There is an air pocket in the coolant (upper engine underneath the manifold). Some GM manifolds have a defective design that allows the coolant to leak from underneath the throttle body assembly inside the manifold. This can contaminate oil (check for caramel milkshake color on dipstick), and cause air pockets to form underneath the sensor---thus the erratic signal.

POSSIBLY A FAULTY THERMOSTAT