What could cause all four 02 sensors codes to continue to show bad?

On computer even after all sensors were replaced? I have a check engine light that has been on before I bought vehicle. I had the codes checked p0054 code and all four o2 sensors are displayed on computer. I replaced all four o2 sensors and check engine light remained. I took it to the local auto parts store to have them check codes and they retrieved the same codes as I had before replacing all sensors.

The salesman said he could reset the codes so he did. I still had the check engine light on so same day I went to another auto parts store and asked to have codes checks to confirm issue. They came up with the same codes and the salesman let me use the hand-held computer to reset the codes myself. Check engine light remains on. The vehicle runs great about 9 out of 10 times.

Occasionally, the vehicle will do something weird. About 1 out of 10 times driving the vehicle, I notice that the vehicle will not allow me to drive faster than 30 mph. Sometimes when this happens, I would be going over 30 mph (and the engine will not response to depressing accelerator and the speedometer will descend. If it drops under 30 mph, then I can accelerate upto 30mph but no greater.

When the vehicle speeds over 30 mph, the engine doesn't respond (still running though). The motor does not run eratic and it seems like the engine has a perfect governor at 30 mph. I will try several times to go over 30 and it will not let me. However, when I pull over and turn engine off and restart the vehicle, there is no longer an issue until about 10 engine starts later.

A friend looked at it and seen the same codes and said he seen an evap leak code (low or High?). I replaced the gas cap and never seen the code when I went to the autoparts store. I don't know if that might be the issue for 30mph problem. However, the check engine light remains on with all 4 o2 sensors.