Hi Folks

Need your help in figuring out what is going on with my HCH 2003. The engine has been hesitating and very weak between 1000-2000 RPM and feels like it is going to stop anytime.

Here are some more facts:---

1)Check Engine light on for almost couple of years now. I am still driving with the light on. My gas cap may have a leak as well.
2)The car had similar symptoms couple of years ago and then they went away.
3)The spark plug were changed 2 months ago. They are pretty good radium spark plug bought at $18 a piece. They were changed by friends friend.
4)The car ran great after the spark plugs were changed until few week ago
5)Few days ago went to Costco. While coming back, the car started with great difficult with lot of hesitation and then stalled after driving for a block
6)Car was towed to a mechanic. They changed fuel pump.
7)The car starts great now. But the hesitation is still there. It is more after I have driven for few miles
8)I am seeing consistent codes P1449, P1420 and P1600. I think P1600 has to do with my IMA light which has been on for last 3 years.

The shop says changing the spark plugs again, EFI fuel cleaning and changing the Oil pressure switch would fix the problem.

Can someone explain what is going on here and if it can be fixed by a lay man. Thank you, best

Nik