Do you ever use these kind of backing tracks to actually write a piece over them? Meaning: instead of just improvising, take several days and actually come up with a set piece of lead guitar over it. This way you won't feel rushed and you can take as much time as you need to write whatever you want little by little.

You can even improvise multiple times and pick the best parts and put them together on one track.

This is just as important as improvising. Because you usually hold yourself to a higher standard when you're taking the time to actually record a set piece like this instead of improvising.