One of the disadvantages of GM patches is that they are often not layered sufficiently to capture the overtones, harmonics etc that occur naturally on many instruments as the attack changes during the performance.

On thing you can do to simulate harmonics and overtones is to fade in and out one or more high notes that add a temporary gleam to the passage. No special rule to this, just experiment. Especially when a solo falls short of the bling you envisioned, try this. Used sparingly, it can add life and excitement to an otherwise dull-sounding track