Feynman wrote at least one book aimed at the graduate level, “Quantum Mechanics and Path Integrals”: https://www.amazon.com/Quantum-Mechanics-Path-Integrals-Emen...

Haven’t really read it so don’t know if its lucidity matches his undergraduate series.

Feynman's "Quantum Mechanics and Path Integrals" is about $18 on Amazon

http://www.amazon.com/Quantum-Mechanics-Path-Integrals-Emend...

That is a serious graduate level book - written in his own style.