Rangers 1996 and up have the "keep RPM" software when shifting but it shouldn't go up.
When you push the clutch in when speedometer is above 5MPH the RPMs shouldn't drop(if foot is off the gas pedal) but will stay the same for a few seconds then might drop to about 1,000rpm but no lower until below 5MPH.
What this does is lower emissions and make for better MPG.
What is the idle at startup, cold engine?
Should be 1,000-1,200rpm
What is the idle after engine is warmed up?
Should be 700-750rpm