2002 chevy blazer issues

My 2002 blazer has been having issues dying while
driving. It will just out of no where lose power and
when I accelerate the rpms drop when I let off the
gas rpms jump up. It'll start back up just fine, go
down the road a few miles and do it again. It
doesn't happen everyday. Also, if I go to the store
and shut it off it won't start back up unless I get a
jump and the cables just have to be on for a
second to get it to fire up. If I let it set for a few
hours it'll start right up. I've replaced the fuel pump,
distributor cap and rotor,  and have had battery
tested and it's good. I'm just at a loss what else it
could be.