Which letter-cluster will replace the question mark (?) to complete the given series?

XDNC, VGOE, ?, RMQI, PPRK

TJPG

Explanation:

XDNC, VGOE, ?, RMQI, PPRK

The logic followed here is :

X → (-2) → V → (-2) → T → (-2) → R → (-2) → P → (-2) 

D → (+3) → G → (+3) → J → (+3) → M → (+3) → P → (+3) 

N → (+1) → O → (+1) → P → (+1) → Q → (+1) → R → (+1) 

C → (+2) → E → (+2) → G → (+2) → I → (+2) → K → (+2) 

So, the letter-cluster that replaces the (?) to complete the series is "TJPG"