Well... if you have flow through the heater core and both heater hoses are hot that feed the heater core. You should have heat! When I say both heater hoses are hot....I mean hot, not just warm to the touch.
And you are saying the truck temp is around 195 or so as verfied through the temp gauage and you are also saying the truck is full of coolant and that the heater control valve works.... all true?
Do you have any expectation that the truck has air in the cooling system?
The heater core could potentially be stopped up or have restricted flow through it. Basically heater cores are replaced when they leak or they become clogged up, like your radiator.
I assume your heater blower motor is working and its just blowing cool air, with the temp setting set to full hot?
I certainly would not replace the heater core on a LC until such time I had looked at all the other issues.
Other issues are..... bad water pump, clogged or restricted radiator, heater hoses setup wrong from engine swap, low coolant, faulty thermostat, bad heater control valve.
What temp is the truck running at now? Does the truck run fine except for the heater issue? Have you driven it extensively, and now all of a sudden no heat?
There is nothing else in the loop but the heater core if both heater hoses that are the return and intake for the heater core are hot, your fan blower motor is working, you are full of coolant, and the temp setting is set to full hot and blowing air at your feet, and the truck is at operational temp.