2002 Mazda B3000 Oil Pressure Gauge fluctuates

I have been having this problem off and on for a while now. If I have my truck on the interstate for more than a few miles and get off on an exit, the oil pressure gauge starts to flicker and the engine sounds like its sputtering when I slow down. It also does this when I'm in stop and go traffic. If I simply tap the gas, it stops doing it. Last week, while slowing down to take a left had turn onto another street the truck cut off. I need some help. Thanks