Hi. I just double checked and G, C and D is Gsus. If you play an Fmaj 7 with a G bass it becomes Fmaj9/G I tried entering sus on the chart instead of 4 and it now plays and sounds right to my ears. But.... I am really just learning this stuff so happy to be corrected.
Sus = replace the 3rd with the 4th note in the scale, So the 3rd note in G major scale is B so wherever B occurs replace it with C. My reference is a very handy book called "The infinite guitar" which you can get in electronic format.Highly recommend as it written in a way that even I can understand!