2000 Windstar pinging P0401 and P1450

[Ferno]

I have a 2000 Windstar.
One day, while driving up hill, I noticed it wasn't doing so well under load. I downshifted manually and it was pinging like crazy. Since the windows were up I hadn't noticed it pinging before.

My son also has a Windstar, but a 2002 (not much different). He had a similar issue happen and ended up replacing the EGR valves and the isolator bolts.

I had the same codes as he did and replaced everything he did and reset my codes.

I drive 50 miles a day up hills and down hills.

The Check engine light stayed off for 3 days but it was still pinging up hills. Maybe not as bad. On the fourth day, with the AC on, on acceleration, the check engine light came on again.

I ran the codes and have P0401 (EGR not sufficient recirculation) and P1450 (Fuel tank vacuum insufficient or something like that).

So, where do I go from here?

What I have done.

Replaced intake gaskets and isolator bolts. Replaced spark plugs, checked and gapped with new ones. Replaced EGR valve. Replaced DPFE and EGR Valve Control Solenoid.

I've checked the vacuum lines. They appear to be in great shape.

I cleaned out the EGR ports in the intake when I replaced the plenum gasket and isolator bolts.

It seems to me the two codes relate to vacuum but is there another reason that I'd get those two codes and the pinging?