For example, the Bludojai Lead amp has sustain for days, assuming drive and MV are high enough.
What no one has mentioned above: Your technique. Introduce a vibrato, and your note will sustain longer - if done correctly.
Make a funny face and hold your guitar in the Air :devilish:
the comp parameter in the amp block helps a bit
I think firmware 10 improves a bit the sustain, I can get musical feedback easily.
I don't know if this is true or why is it happening, but this is what I'm experiencing