The FAA actually *recently* changed them for DRVSM back last November AND September 1st.
This is what fltplan.com lists:
NO DME
/X NO TRANSPONDER
/T TRANSPONDER WITH NO Mode C
/U TRANSPONDER WITH Mode C
DME
/D No TRANSPONDER - DME ONLY
/B TRANSPONDER WITH NO Mode C
/A DME AND TRANSPONDER WITH Mode C
TACAN ONLY
/M NO TRANSPONDER
/N TRANSPONDER WITH NO Mode C
/P TRANSPONDER WITH Mode C
AREA NAVIGATION (RNAV)
/Y Loran, VOR/DME or INS with NO TRANSPONDER
/C Loran, VOR/DME or INS with TRANSPONDER & NO Mode C
/I Loran, VOR/DME or INS with TRANSPONDER & Mode C
Advanced RNAV WITH TRANSPONDER AND MODE C (but not RVSM cetrified)
If an aircraft is unable to operate with s transponder and/or Mode C, it will revert to the approriate code listed uder Area Naviagation
/E FMS with DME/DME and IRU position updating
/F FMS with DME/DME updating
/G GNSS, including GPS and WAAS, with enroute and terminal capabilities
/R RNP,Aircraft meets the RNP type prescribed for the Route, and Area concerned
RVSM (Reduced Vertical Separation Minimum)
/J '/E' with RVSM
/K '/F' with RVSM
/L '/G with RVSM
/Q '/R' with RVSM
/W RVSM
/A DME AND TRANSPONDER WITH Mode C
/B TRANSPONDER WITH NO Mode C
/C Loran, VOR/DME or INS with TRANSPONDER & NO Mode C
/D No TRANSPONDER - DME ONLY
/E FMS with DME/DME and IRU position updating
/F FMS with DME/DME updating
/G GNSS, including GPS and WAAS, with enroute and terminal capabilities
/I Loran, VOR/DME or INS with TRANSPONDER & Mode C
/J '/E' with RVSM
/K '/F' with RVSM
/L '/G' with RVSM
/M NO TRANSPONDER
/N TRANSPONDER WITH NO Mode C
/P TRANSPONDER WITH Mode C
/Q '/R' with RVSM
/R RNP,Aircraft meets the RNP type prescribed for the Route, and Area concerned
/T TRANSPONDER WITH NO Mode C
/U TRANSPONDER WITH Mode C
/W RVSM
/X NO TRANSPONDER
/Y Loran, VOR/DME or INS with NO TRANSPONDER