G to Dsus4
How to transition from a G chord to a Dsus4 chord.
The G → Dsus4 transition is the same I → Vsus4 move in the key of G or any key where you're playing an open G shape.
Chord shapes
By playing the G chord in a full G shape, the transition to D becomes a lot easier. Your fingers need to move from the top of the fretboard to the bottom, while maintaining your third finger on the B string.
GFull
Dsus4Full
Anchor fingers: finger 3 on B string (fret 3), finger 4 on high e string (fret 3)