2013 Subaru outback 2.5l limp mode & cylinder misfire codes

Bought used 4 years ago. Vehicle has no Cat Conv, they are not required in
MO. I am good about regular preventative maintenance, I want this car to be
my last. First went into Limp Mode 2 years ago, mech said throttle body.
Replaced throttle body. All good for over a year, then starts going into limp
mode again.  Gas pedal code, replace gas pedal. Still going into limp mode.
Change spark plugs & coils, still going into limp mode. Turning car off for a
few mins usually resets the system, but ridiculous mystery now.  Limp mode
again Dec 31, had to disconnect battery for 30 mins to reset - but now the
car is hesitating every 1/4 mile. Throwing cylinder codes P0300 & P0301,
other times code P0303.  Subaru dealership can't find the problem after a
whole day (but will continue attempting to diagnose if I spend $1300 on
parts) - they say  next thing to try is timing. My guy replaces timing chain, Still
rough, code P0303. A few days later, seems okay, smoother idle - no codes.   
Drive onto the street, starts hesitating again, codes P0301 & P0300.
SOMEBODY PLEASE HELP!! I am a single 64 y/o retiree on Soc Sec & no
one - including Subaru "professionals" - can help me, everyone is stumped...   
:(    TYIA for any solutions or suggestions