So my 2012 Mazda5 Sport manual transmission (94k miles) has developed a strange issue. I ran the spark plugs too long and they misfired a bit but when I changed them the error code left but it didn't stop all the issues. So now when I'm on the freeway in 6th gear and go up a hill I will get little hesitation stuttering, I have to downshift to 5th keep the RPMs up so it won't do it. With the air conditioning on it's worse, I have to drop to 4th. Yesterday I was going up a hill in 6th, 60mph so like 2400rpm and it started again. Recent service is new plugs, air filter, oil change, serpentine belt. Has no issue with higher rpm, i can run up to redline without any hesitation or issues, just that lower RPM stutter when a load is present. Any ideas? Thanks for reading.
