Gary,
It 'wears out' after use, but how soon seems to vary. It is not as effective on lacquers as it is on enamels and acrylics, and it may seem to stall out if you use it on lacquer.
It usually works for quite awhile (weeks) before losing effectiveness, but that also depends on how much it's used during those weeks.
Regarding your issue, try some 91% alcohol on that truck cab.