Q: I have been experiencing a lack of power at acceleration that does gradually increase. Is it my fuel filter?

I have been experiencing a lack of power at acceleration that does gradually increase and catch up to the speed of traffic (typically at 30-45 for 30 seconds and then get up to 55.) This is an intermittent problem. My check engine light does not come on.

My fuel filter has not been changed, and my air filters were only recently done. I drove it across the country and it cleared the EGR valve that caused the check engine light to come on. A mechanic said one of the sensors for the air intake valves is bad. He "test drove it extensively" and did not have the same issue. I don't understand how. It's obvious to me.

I may not even have this car in a month, but need to reliably drive my kids around. Could a fuel filter replacement be the answer? What about diesel fluid? Anything else? I don't have a lot of funds to throw at this, especially if I won't be able to keep it.

My car has 85000 miles.
My car has an automatic transmission.