On the 96+ SCFI motors, one of the earliest things I would recommend to anyone is to clean the MAF sensor. If you have run or are running an aftermarket oiled air filter (ex. K&N), there is a good possibility that the MAF sensor elements have been coated with the oil and are feeding false readings to the PCM which can cause a whole mess of problems.

In the case of inaccurate readings at a specific RPM (I assume a speed was mentioned because you don't spend hardly any time at this RPM in any other gear, but it should be repeatable at this RPM in any gear none the less), I would agree, the MAF sensor itself is at fault.