The amount of oil that the 2001 Chevy Silverado takes depends on the size of the engine in the truck.
For a 2001 Chevy Silverado with a VORTEC 4300 V6 it would take 4.5 quarts of oil and for a 2001 Chevy Silverado with a VORTEC 4800 V8 or a VORTEC 5300 V8 engine it would take around 6 quarts of oil.
So get 6 quarts of oil just to have enough and then add 4 quarts of oil and then let the engine run for a few minutes and then shut it off and let it sit for 10 minutes to allow the engine oil to settle down into the pan and then check it again.
Then add a little at a time until it's filled so you'll avoid overfilling the engine with oil which can be damaging.
If you overfill the engine oil you need to drain off the excess engine oil.