Had a '92 Jeep Cherokee XJ for a while. It would start and run intermittently. That is, it would run fine as long as it started, it just didn't always want to start. I went the computer and started reading up on causes. It boiled down to one of two things; the ECM or the Crank Position Sensor.
Well the CPS was all of $35 plus tax, and the ECM was over $100. I bought the cheaper part, and went home to replace it. I pulled the old one off, and it looked brand new (I had just bought the Jeep from my mother-in-law, and she'd had a bunch of sensors replaced trying to fix the problem). So, I put the old one back on, and took the new one back, having not installed it.
Then I ordered the ECM. Took all of five minutes to replace, and it ran great, and started every time. No issues.
{That is, it would run fine as long as it started,}
Read the OP post again, that is not the case here. My advice is to not shotgun parts as your Mil did especially on someones DD (daily driver).