It is a struggle to become a great guitar player when you don't have ear training skills. However, it's probably not for the same reasons you might think...
Most guitar players believe that ear training only refers to identifying notes, chords or scales... but it's much more than that! Developing a good ear as a guitar player also means being able to hear your mistakes while playing at fast speeds. This helps you fix mistakes that occur ONLY at fast speeds (not at slow speeds) in order to help you improve your technique. A guitarist with a good ear is able to hear mistakes of sloppy playing, identify what notes are sloppy and WHY they are sloppy.
Use the following ear training exercise to improve your ability to hear mistakes in your playing:
Step One - Choose a phrase, lick or riff that is no longer than 10 notes that you'd like to improve.
Step Two - Determine the speed at which mistakes appear while playing the item you chose in the previous step. Use a metronome to get the exact tempo.
Step Three - Reduce the tempo by 5-8 beats per minute and play through the item for one minute without stopping. While you do this, focus your attention on one specific note. Pay close attention to listen for any mistakes or imperfections in that note.
Step Four - Think critically about what is causing any mistakes for the note you were focusing on in the previous step. Play through the item again while making any necessary adjustments to fix the mistake(s) that made the note sound sloppy.
Step Five - Play through the practice item for one minute without stopping while focusing on a different note. Use this as a way to identify the subtle mistakes you make that you might not notice while playing normally.
Repeat this process as many times as needed until you have cleaned up every note for the practice item you chose. Then set the metronome up to the speed where the mistakes originally appeared and do this exercise again. The more you repeat this exercise, the stronger your ear becomes for identifying mistakes in your playing.
Practice using this creative approach consistently and watch as your guitar playing gets cleaner and cleaner every session. Do this for several weeks or months and your guitar playing goes to a whole new level where it becomes easy to play fast.