My sons Pathfinder will suddenly slow down or lose acceleration while driving

What is your question?

I have had it a mechanic several times to solve the problem and check codes. The last time he suggested I put new plugs and wires on which I did and it still does the same thing. I want to sell the car but don't want to pass on the problem.

What makes this problem better or worse?

Seems to happen after running fine for first 15 minutes, but varies

How long has your 2006 Nissan Pathfinder had this problem?

A long time