Oddly cuts off in reverse and park sometimes....

When I bought my car it had 96,000 miles on it
(bought it Feb. 2016) It ran great with no problems.
Being that it had low miles I figured it had been just
sitting and expected to have the fun of maintenance,
changing out certain parts, tires, etc... SInce I've had it
I've changed the waterpump, belts, thermostat, new
housing on the radiator, throttle position sensor, idle air
control valve, brakes (rotors, drums, shoes, pads,
calipers) tune ups, change of all fluids.... Runs great,
the big mystery I have is sometimes it cuts off in
reverse or park??? I've checked all hoses, changed
filters, been to different shops and for some odd
reason no one can figure out why my car is cutting off.
It starts right back up with no problem though...