Mass Air Flow Sensor replacement?

[hokie]

For the past 4 weeks my 96 4-Runner (4WD 3.4L) has been experiencing a sluggish engine along with a drop in gas mileage (from ~19/20 mpg to about 15 mpg). After noticing that the passenger side floor board had gotten unusually hot after a long trip, I immediately got in to drop it with a mechanic that I use. His first inkling was a clogged catalytic converter, which would explain the hot floor board and degraded performance, but after replacing it, I didn't notice a change. The mechanic is pretty good at trouble shooting, but I think he's to a point where it is buy and replace (trial/error). I am not getting a check engine light and he has put a sensor checker on the vehicle and he didn't receive any faults, but when he checked the MAF sensor, he noticed that there were glitches in the readout and the sensor was out of tolerance. So, I'm going with the Mass Air Flow sensor as my next move, but at $250.......an expensive educated guess.

Two questions:

1) Anyone had an experience like this......and what was the fix for you?

2) I've read that Oxygen Sensors should be replaced every 100k miles...good or not. Any thoughts on this?

Any help would be appreciated.

thanks