Car: 91 hatch with a Z6 and OBD 1 swapped in, new distributer, fuel filter, and O2 sensor,cam and ignition timing was recently set, no CEL's. Also has O2 meter installed and fuel pump controlled by a toggle switch (long story). Problem: When I first start it and drive it around town, it's just fine. If I were to take off down a highway and hold it at a constant speed, it will be fine for a mile or so, and then almost like someone flipping a switch, the O2 meter will go super lean and the engine will start to bog down and chug terribly and not want to rev past 3k. If I were shut off the engine for only a few seconds and then re-start it, it will act like nothing ever happened until I go a few more miles at a constant (higher) load (as in on a highway) and then do it again. Another (and quicker way) to induce this is to do a wide open run through the gears. While I'm going wide open and shifting it will be proforming just fine, but as soon as I take my foot out of it, it will be super lean and bogging down again, requiring a re-start. Because of the suddenness of it, I would tend to think that it might be some sort of sensor or something electrical, but there are no CEL's. Another thought that crossed my mind is that the fuel pump is on the way out....but then wouldn't it be doing the "bog mode" almost at random instead of after the engine being under load? Any ideas?