Last night I got the replacement MAF o-ring in the mail and installed it. The old one was pretty stretched out and didn't seem like it was sealing very good. The new o-ring did help out a small bit. It's marginal, but I do feel a difference in idle and throttle response. But the major vibration that occurs in 5th gear around 1500RPM, while cruising along at 40mph, is still there. It's really like the engine is chugging or dropping out for some reason. Low fuel, low air, I don't know. Feels starved at that specific RPM or speed.
Beginning to think that maybe the issue is the product of several things: lazy o2 sensors, worn out throttle body, clogged EGR, etc. Seems like I have several options to try, but I just hate to throw parts and money at it and hope it fixes it.
Once the cold weather breaks in the next few days, I will try to get under the car and inspect tie rods, control arms, and CV joints.
One way or another I'm gonna figure this out!!!