1999 jeep cherokee

My vehicle will sometimes automatically shut off I
suspect it's my fuel pump because I fixed the
misfire it was having. changed out the spark plugs
wires and cap and rotor.  It will turn off sometimes
while I am just rolling down the road or going at a
constant speed on the freeway. I have to prime my
car to her three times for it to start easy otherwise it
revs for like four or five seconds.  When I attached
A fuel pressure gauge is when the engine is running
it is at 49 psi and after the first prime  of the engine
it is at 35 PSI.  When I prime it the first time it goes
up to about 15 that's if I haven't  primed it in a few
minutes.  To prevent my car from turning off when I
can hear that it's about to turn off or Certs chugging
I will accelerate and it will stop it . I want to know
why my vehicle will sometimes turn off
automatically.