I've been reading a bit about this problem.
You are right, if it was running without detonation before, something must have changed.
I'd start looking at everything "air delivery" related and begin with cleaning and inspecting the Mass Airflow sensor.
Also, check the air intake for leaks and all of the vacuum hoses and the intake manifold for vacuum leaks. Dont forget to clean or replace the PCV valve and inspect the grommet and hose for leaks.
After all of the air related things are checked. You'll want to turn your attention to the fuel delivery system and run a fuel pressure test.
Something is "tricking" the computer to make the engine run lean. Check all of the" free" stuff first...
Detonation under load at about the same speed as you was one of the symptoms I had when I had a weak COP. No codes thrown but I could feel a miss at those speeds as well. Accelerating made the miss/ping disappear.
I found it by data logging with my SCT.
If you have a code reader that detects pending codes you might be able to see them there.
Just a thought if the usual suspects don't solve the problem.
That's the whole problem IMO. It could be so many different things. If you bring it to a mechanic and they start throwing parts at it.. It will expensive fast. If you have limited savings, then it will prolly eat through that pretty fast.
Yes I edit my posts a lot, auto correct likes to sabotage me!