Help with Trouble Codes

I've been reviving a low mileage 91 with a 2.3 that sat in my neighbor's yard for a few years, and so far it's gone pretty well: New fuel pump, timing belt, brakes, water pump etc. However, the beast keeps losing power at unpredictable moments, as though it was a fuel problem, and then it recovers nicely after I pull over for a moment or two. Finally I took it to O'Reilly's and they ran the computer and came up with two codes: 33 - "EGR Valve opening not detected," and 51 - "ECT Indicated -40 F/circuit open." Not sure if either points to my problem or what to do next. Start replacing things? Further testing? All informed suggestions welcome. Thanks. Uncle Buck

I'm not the most informed but my 91 Ranger had a similar issue and my EGR Valve went bad. I replaced it and it seemed to do the trick. Pretty inexpensive thing to try