My truck has been pinging for sometime and 91 octane has not helped. It only pings occasionally when driving up a grade. Spark plugs and wires are good and I have no check engine light or codes. However, I added Lucas octane booster to 91 octane and the pinging went away. However, I do not want to pay $11 for a bottle of Lucas every time I fill up. How can I fix this?? Please help.