when i am driving my 89 dakota the oil pressure is fine but when i come to a stop it go down sometimes all the way down if sitting there long enough.. I noticed one time i put it in park and it went back to normal then put it in gear (foward and revers) and it goes backdown

 

check the oil pump, my friend bought a dak that had a "bad motor" and it showed the same symptoms as yours, turned out the screen in the oil pan needed to be cleaned and he put a new oil pump in as well.

 

Replace the oil pressure sending unit first...that's the easiest and cheapest place to start troubleshooting.

 

k thanx i will someone else said somethin about the oil pressuresending unit il check on that you know about how much that runs and it is easy to replace?