95 jeep Cherokee shuts off on bumpy roads

I have a 95 Cherokee.  It's had this problem for a month or
so, it quits when driving on very rough pavement, and
occasionally on dirt roads.  The rough pavement in
referring to is rougher than most dirt roads.  It has always
started back up, sometimes right away sometimes I have
to wait 2-10 minutes. I use it to deliver mail.  It only does
this on the mail route, never on the highway or in town or
anything.  Changed fuel filter first, then fuel pump.  About
a year ago it wouldn't start and I changer the cam sensor,
crank position sensor and coil.  Any ideas what could be
wrong with it.  When it dies, sometimes it runs real rough
first, most times it's just like you turned the key off.  
Sometimes it only does once a day, sometimes it's every
100 yards of so.