My Tahoe will sometimes leak oil at interstate speeds. I can’t tell where it is coming from but it doesn’t appear to be the pan or valve covers. It drips down and burns off on the exhaust pipe behind the bell housing. Also my oil pressure gauge fluctuates between about 30 and 50.
You need to put the truck on jackstands and get under there, on a creeper
Good chance you’ll find the leak
It could be valve cover gaskets leaking, allowing oil to drip onto hot exhaust manifolds, causing smoke
Could also be the engine oil pressure sensor leaking. This would be a very fast leak, though
Could be the cylinder head gasket(s) leaking oil externally
Could be lots of things
please let us know what you find