maf sensor question

[mss5413]

If anybody has ever run a maf sensor test according to the service/repair manual I would like to compare my results. The manual suggests that the sensor puts out ~4.0 at 4000 rpm, mine holds at 3.0v(4000 rpm), this does not seem right at all and my car lacks power and idles rough at any random moment. I have been buying the last two sensors salvage and they give similar readings of 3.0v. If I hit the accelerator hard at 2500 rpm it overloads my meter and continues at 3.2v. Any input would be greatly appreciated.It's just a very expensive part to replace new, and I want to make sure I have eliminated all other possible causes.

Power to sensor is ~13.8 volts, engine onpretty sure the ground is right above thermostat housing, the sensor stayed on with the ground disconnected(strange )that pretty much sums it upAm I forgetting something?