My '01 has about 130k miles on it.

Just in the last few weeks I've noticed a lot of rocker arm noise from the driver's side rear of the engine. It goes away a second or two after the engine comes off idle.

I've had the truck for four years now, and I seriously doubt the oil pump has been replaced.

What's the likelihood the pump is cracked?

Roughly how many hours does it take to replace the pump?

 

Plan on a solid day if you take your time.

I would check the actual oil pressure before pulling things apart. Not only to verify that the pressure is low but also to compare before and after readings.

 

Cracked - maybe. Needs replacing? Yes.

I would also replace the timing chain, cam gear, and crank gear while you're in there. Couldn't hurt to also check your camshaft end-float and either fit a new thrust plate or cam+lifters if out of spec.

Check the oil pump housing tolerances as per the Overhaul manual and look for any scoring or gouges. If out of spec, the front cover needs to be replaced.

I stripped the oil pump cover screws, so replacing with flat socket head screws is a nice upgrade.

Pack the pump with vasoline and/or assembly lube before putting it back together.