If you know how to play notes you can play a lot of different songs. If you have started to practice slides you can include that in your playing. If you have the note playing or slide playing ability each time you take a new song your skills are not the problem.
It is often just a memory issue if you’re frustrated with lack of progress.
Even without the instrument we can practice a new song. All I need to do is keeping on recalling the progression of the notes in my mind, checking till I have them all correct.
I do not require the instrument because I know already how to play a note or a slide. But if I do not know which notes to play in which order and how it sounds, then my skill doesn’t matter. I just don’t know what I have to play with or without the instrument
If you’re trying a song and if you’re feeling frustrated see if you are trying to remember too much in one go.
Instead of thinking it as a music problem consider how you would memorize this piece.
I can only remember so many notes in one time. So I remember a few of those notes and try to memorize them before getting to the new lines. It is better for memorization to not take too much and keep on repeating but instead take a little bit, recall, keep on filling up the gaps, clarifying the picture.
If you’re really getting frustrated with a song and finding it difficult to memorize maybe you are not interested in that music at all.
This happens quite a lot especially since generic guitar lessons are available or there is just a simple mismatch with the person’s culture and interest.
Next time you take a song instead of trying to play the full line, see what are the notes used and the movements to connect them. See how much of it you can really memorize in the first go. Take only that much, consider it as a memorization problem, pace yourself for better practice results.