The first thing that you need to do is verify that the Oil Pressure lamp lights when you turn the ignition to On, but before you start the engine. Then, watch out for the light, especially when the engine is idling. It comes on at a very low oil pressure - 6-8 psi.
The ideal way to check for sludge is to drop the oil pan, inspect and clean as necessary. An easier way is to pull the valve cover to see if any sludge is present. If it's present, drop the oil pan.
Some have success with running Auto-RX treatments which will eventually disolve the sludge, but will not clean non-sludge particles off the oil pan filter screen. If there's too much junk on the screen, the oil flow will be reduced and cause major problems... Ron