Engine won't rev more than 3800 RPM Rev limiter stops it

I have an 06 4-door sedan automatic. We bought it used several years ago for my handicapped son. Not long after we bought it the check engine light came on. It seems to be a Cat converter and or O2 sensor issue. We have replaced all of that to no avail. over the years we have replaced the throttle body and the throttle (Accelerator pedal) control, spark plugs, coil packs and wires. Up until a week or so ago it was running fine. We never did find out why the check engine light was on constantly because there were no codes, so to placate my OCD son we had the bulb taken out to keep him from trying to throw unnecessary parts at it. Now two weeks ago the crank position sensor failed and was replaced by our local independent shop and codes cleared. A day or so after that my son complained that it was bucking and jumping. I drove it and sure enough under WOT when the tach hit about 3800 rpm what seems like the rev limiter kicks in. I stopped put it in park and about 35-3800 rpm was all it would do. I took it back to the local shop and they had it for about a week and threw up their hands and said it would need to go to a stealership. I did and they have had it for a day and a half. Last report I got from them was "WE ARE STILL CHECKING."
HELP!!!

What codes are currently present, if any?

The engine could of also been misfiring, which would cause it to buck at those RPMs, especially at wide open throttle. You should replace the actual bulb in the check engine light; a flashing CEL would mean a misfire condition is occurring.

No codes, active or logged
It is at the Stealership and even they are scratching their heads.