Allostery predictions algorithms, which are based on mathematical rigidity theory, provide a mechanical interpretation of allosteric signaling in protein structures. Rigidity Transmission Allostery (RTA) methods are designed to predict if perturbation of rigidity at one site of the protein can propagate across a network and in turn cause a change in rigidity at a second distant site, resulting in allosteric transmission. Here we focus on the application of RTA on allosterically driven functional dynamics in G-Protein Coupled Receptors (GPCRs). We show how ligands trigger allosteric changes that propagate to functionally important regions; the role of beta-gamma subunit in G proteins as critical facilitators of allostery within the ternary complex with adenosine A2AR; the role of differentiated allosteric pathways in GPCR promiscuity and selectivity mechanisms in A2AR in the presence of different G protein subtypes. We combine 19F-NMR and RTA to delineate allostery and distinct key functional activation and precoupled intermediate states in Adenosine A2A GPCR complexed with heterotrimeric G-protein. NMR showed that binding of G-protein stabilizes a precoupled activation intermediate state and two distinct active states which facilitate nucleotide exchange by full or partial agonists. RTA showed beta-gamma subunit in G proteins is critical in facilitating allostery within the ternary complex. We present results on several GPCR structures and recent work which investigates the selectivity and efficacy in A2AR in the presence of different G protein subtypes.