Loss of power while driving

My 2011 Equinox loses power while driving it. It feels like it is running out of
gas. When the I step on the gas to get it going nothing happens then it will
suddenly "catch up" with itself. This happens at various speeds and is very
intermittent. I have done the following repairs to the engine. New spark
plugs, new air filter, new upstream and downstream oxygen sensors (these
had a code showing), new intake and exhaust VVT sensors, new mass air
flow sensor, injector cleaning service (at a Chevy dealership), new throttle
body. The system fuel pressure was found to be 58 psi with the key on and
engine not running with only 4 psi drop in five minutes. While running it has
58 psi  and sometimes will drop to 40 psi while running. Any suggestions as
to what my cars issue would be? Could I have a fuel flow problem from my in
tank pump?