Oil pressure going up and down?

my oil pressure on my 96 jeep cherrokee reads a little high first start up its pegged at 60 or so until it warms up then it drops to about 40 then when driveing it goes up to about 64 or so then when i slow down it goes down with the engine rpms to about 40 when stoped but it kinda jumps a little like goes 40 then 45 then 41 then 45 then when i hit the gas it goes right back to 64 or so plz help not 100% whats going on