There is certainly no need to continue lessons with an instrutor if you feel they aren't doing much for you. Can you go less frequently - once a month? Maybe to ease into the transition? Or do you feel pretty certain at this point?

Years ago I quit lessons because I felt like I was going nowhere. I spent most of the time sitting there watching him transcribe music for me. We would move onto something else before I had what we just did even remotely down. I got frustrated, stopped practicing, and it went further downhill from there. One day I decided enough was enough.

Oh how I wish I knew then what I know now. However, on the plus side there are wonderful resources here today (GT, this forum, etc.) that as long as you are disciplined and focused you can get a lot out of.

If you find quitting leaves a gap, you can always go back, right?