98 Nissan Frontier 4WD Oil light sometimes blinks

Hi

Ive got a
98 Nissan Frontier 4WD with 140k miles

a few weeks ago my oil pressure warning light would flicker on sometimes. It would only blink when I was accelerating at moderate speeds. If I accelerated hard it would not blink at all.

I thought maybe the oil had gone bad, since it at been about 4-5 months since my last change (only 2k miles) and I do not drive my truck on the weekend.

After changing the oil and oil filter, the problem disappeared. But then after being parked over the past weekend, it started again yesterday morning.

Could my oil pump be going bad or does it sound like something else?
Would a mechanic be able to most likely diagnose the problem by looking at it, or should I take it to the dealership?
If I need a new oil pump, is there any preventive maintence I should go ahead and get done, while the mechanic is there. (Like replacing the timing chain)

thanks for any advice