Something else to consider, Piston slap is usually worse when cold and goes away when the pistons get up to temp and expand. I have never heard piston slap get worse as the temp rises, sounds more like a bearing / clearance issue to me.

Your piston is definitely not hitting your cylinder head.

If you replace the engine, remember that a new / reman engine would likely cost every bit as much as the car would be worth in good running condition, not to mention the cost to install. I would just go with a good used engine and call it a day.

I guess, but I can always buy new parts for it too and rebuild it.

How do you know it is a "piston slap"? It may be a rod bearing or the valve floating and being slapped also. I suggest a quick top end tear down and do an exam of the cylinder walls. It it is a broken ring, or you have a grove in the wall, consider a rebuild vs. pick-a-part type swap of a crate engine. You can trade in your old tired motor for a refurbished one for around a grand I think. I love my 04 Pontiac, great ride, wonderful mileage in the road, and is a sound vehicle. AND no car payments.

Yea I recognize that noise...its most likely that the rubber in the harmonic balancer is toast. You can easily confirm this by running the engine with the serpentine belt off...if the noise lessens then that is the problem since there is less load on the balancer itself.