So here is what I found. I went to a site that has an archive of owners manuals & entered Lexus RX350 & as luck would have it they did have a manual. The only question is for what year the manual is for but I'm thinking for my issue the manual has not changed regardless of the year.
The RX350 does have two cruise control modes, one called "constant speed" mode & the second called "vehicle to vehicle distance control" mode. When you first turn the engine on the default mode will be the vehicle to vehicle distance control mode but it can easily switched to the constant speed mode by holding down for one second the cruise control button.
