2002 Explorer bucking problem

I own a 2002 Ford Explorer 4WD with a 4.0 V6 and 80k miles. Recently I have noticed an intermittent problem when the engine is at a low RPM usually in OD between 40 and 55 MPH the engine will buck or mis fire a couple of times when driving a steady speed or accelerating slightly, it will become less noticable after I press the gas and drive the RPM's up as it downshifts and accelerates, this is not a constant bucking but will do it 1 to 5 times while in this RPM range. I have changed the air filter every 20k miles, just had the throttle body and injectors cleaned, I also cleaned the MAF sensor. I have not noticed any type of vacuum leak. No engine light has come on while I have had this problem. It has a very slight (barely noticable) but also intermittent mis during idle, but when I raise the RPM's at idle it runs smooth. At $100+ I am hesitant to replace the MAF sensor without being quite sure it is at fault.