For the past 2 months after i drive for say 20 miles or so .. when i come to a stop or take my foot off the gas and "coast around a corner " the oil pressure gauge will drop to zero and warning will sound if i hit the gas it will come back up

when the car is idling it is around 750 rpms or so maybe a bit less..

Is my oil pump going ?

it has happened prior to and after oil changes..

try getting stp fuel injector cleaner. I had the same problem on my 94 JCL. It would really idle rough when i came to a stop. Also might be the Idle Control Valve.