Already Cooked for 1hr 15 min at 300.
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Pull it out; tent it w/ foil. just curious- what was the weight of the roast?
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In addition to tenting it while it rests (the bubbling internal juices will redistribute. You can hold it in a slow oven at under 150F.
If you're going to follow Pierino's advice, you better know for certain that your oven is capable of holding that temperature.
The thermostats in a lot of consumer-grade ovens aren't able to reliably maintain such low temperatures.