P0325 and P0300 codes

[#z'sx#]

I'm so glad I found this forum! I just lost my job and, of course, my XTerra started acting up a week later. The serpentine belt was frayed, so I had that replaced. The knock sensor and misfire codes came on. The repair shop replaced the spark plugs and fuel filter and erased the codes so the check engine light was off. I drove it for about 1 min before the same slipping or chugging started up again & the check engine light came back on. I noticed on this forum that there was a recall that could be related? The repair shop suggested filling up with high test and driving some more to see if it clears up. Would this hurt the car?Thanks so much!!