You are correct to be going to the 140.90.88.142
(also ftp://tgftp.nws.noaa.gov). Go to
SL.us008001/ST.opnl/MT.ruc_CY.XX/RD.YYYYMMDD/PT.grid_DF.gr1
where XX is the model cycle (00-23) that you want. Note:
I take NO responsibility for this naming convention.

 You'll see 4 different types of files for each of
the different forecast hours. The ends of the file
names refer to the following:

 bgrib - output on native levels (grid 236)
 sgrib - surface output (grid 236)
 us40km - output on pressure levels (grid 236)
 us80km - output on pressure levels (grid 211)

I have no idea why all of the file names contain
the word 'press'.