There is no "2nd reserves" unit, and there are no corps size signal units. There are probably numbered companies and a headquarters and headquarters company (HHC) under the 454th Chemical Battalion. Reserve Regional Readiness Commands (RRC) have all sorts of units under them. RRCs replaced Regional Suppport Commands awhile back. We need more info to put together a bumper number for you. An example could be your truck belonged to 340th Chemical Company, 454th Chemical Battalion, 290th Regional Readiness Command.
However, I can't find either a 290th RRC or a 290th RSC. There are several chemical battalions under the brigades within 335th Signal Command, but I don't see the 454th task organized in there anywhere either under current or past listings. Reserve command relationships can be very confusing as they are task organized purely for adminstrative function, they don't fight the way they're organized in CONUS.