With all due respect to a computer science grad from a lowly auto enthusiast
(and an electronic engineer, but that's besides the point), the computer
would be the last thing to suspect in your case. It has decent self-test
capabilities and in the rare event when it fails so badly that it can't
diagnose itself, you won't get any codes at all.
I am not familiar with your engine, so it's hard to give advice on your EGR
problem. You mentioned an EVP, as if it were a position sensor on top the
EGR valve. But if Autozone put pressure (or vacuum) to test it, it's a PFE
(a pressure sensor), not an EVP. Assuming that they know what they are doing
(which I would doubt), the failure may be in the EGR control solenoid. Or
you may have carbon deposits in the valve, the EGR tube, or the passages,
blocking the flow. Also check the pressure sensing tube connected to the
sensor and make sure that it is not blocked and has no leaks.
50 Ohms is way too low for an ECT any any temperature. It should read
something on the order of 2 KOhms with a warm engine. Before you run to
replace it, make sure that you measured it properly. Was that an analog
multimeter that you were using? You would not be able to read 50 Ohms with
any accuracy on 100K scale with such instrument. Switch to a lower scale and
repeat the measurement. And verify that the instrument reads zero with the
probe leads shorted together.