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did you just get the truck? what/when started these problems? are you sure its not a faulty gauge or sensor? is it an aftermarket sensor or gauge?
New "wrong" water pump might be to blame. The newer style runs in reverse although from the outside they look the same... My $.02
for testing the gauge http://forum.73-87chevytrucks.com/smforum/index.php?topic=25339.msg300093#newfor testing the sensor http://forum.73-87chevytrucks.com/smforum/index.php?topic=29996.0 (its for the ecm, but it should have about the same outcome with the ohms raising)
Just to clear up the water pump differences, the pulleys do not interchange. The hub flange and bolt pattern were changed when they reversed rotation. When you say leaks were "plugged" that means what exactly? T-stat was replaced? Upper and lower hose gets hot?
And check the exhaust for excessive backpressure. When an exhaust becomes restricted it can cause an engine to heat up rather quickly and overheat under load, depending on the severity of the restriction. Make sure there isn't a restricted muffler or catalytic converter and that a double wall exhaust pipe hasn't collapsed internally.Edited for clarity.
Sounds like you need to take it to a shop and have those core plugs replaced. You probably have a clogged radiator if you used leak stop.
Inspect the front of the radiator for flattened fins that obstruct airflow. Straighten bent fins as needed. If the fins exhibit evidence of disintegration, replace the radiator or have it recored. Start the engine and bring it to operating temperature. With the engine running, place your hand against the driver side (left) front of the radiator and drag your hand toward the passenger side. You should feel a gradual decrease in temperature with no "cold spots" as you drag your hand across. Repeat this process across the entire front of the radiator. If you feel an uneven change in temperature (cool spots) the radiator is plugged and needs to be rodded and repaired, recored or replaced. There should be a net drop of about 20° F between the radiator inlet and outlet.Remove the fan shroud. Using a high flow air nozzle connected to a +120 PSI air source, methodically blow the accumulated bugs, feathers and crud out of the radiator fins being careful not to flatten any fins. If the vehicle has A/C, remove the upper radiator support plate to reveal the gap between the condenser and radiator and use a 36" long air wand to blow out the fins. Repeat the process on the condenser.And, I agree...Quote from: VileZambonie on September 22, 2017, 05:49:21 AMSounds like you need to take it to a shop and have those core plugs replaced. You probably have a clogged radiator if you used leak stop.Replace the core plugs and followed by a thorough flush. Stop leak in a compromised radiator exacerbates overheating issues. It may not be the primary cause, but adding constipation sauce makes a bad situation worse.