I have a 98 yukon with a 5.7l 350? My orignal problem was that it had a compression of 90 on #5 cylinder. Since then I have found I have a blown head gasket. It was recommended since I had another block(crate engine) to just swap them out. What all is recommended to change when doing this? I know the plugs, wires, rotor, d cap, coolant, and oil. Is it anything I missed? Also, I was told that some sensors may need to be changed. If so what are they? All I know the guy said something about temperature but he couldn't name the sensor. I want to get this right so please HELP!

The sensor he's referring to is the coolant temperature sensor (CTS) and, yes, that should be replaced with a new one.
And a new thermostat and radiator cap. Have the radiator tested for sufficient flow. A new water pump. Both radiator and heater hoses, and the drive belts.

You may want to consider a high output oil pump and perhaps install an oil cooler during this swap.

Ok Thanks for the help and just wondering why change the radiator cap?

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Originally Posted by damdash

Ok Thanks for the help and just wondering why change the radiator cap?

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For the same reason the thermostat gets replaced: it gets weak over time and loses it's ability to seal and purge air properly.
It's a relatively inexpensive part and considering how vital it's function is, gives peace of mind knowing that the cooling system will be full and operating properly.