how to time a 96 chevy k1500 5.0?

Its all done by the computer so there is noting you can do to change it. All rotating the distributor does is aligns the rotor with the terminals. If someone has messed with it there are special tools and equipment to get it set but the DIY method is to take an old distributor cap and hack out the plastic around one of the terminals so you can see the rotor. Re install the cap connect a timing light to that terminal. Start the engine and point the light at the cap. The light will flash when that wire is firing. When it fires you want to rotate the distributor so the rotor is pretty well centered on the terminal.

Those 'crab' style caps are horrible for moisture and carbon problems problems causing cross fires.

An OBD-II compliant scan tool is required for that engine,best checked by a mechanic or crossfire may result.