2002 Malibu Rev/Surge/Chuggle

I drive a 2002 Malibu with the 3.1L V-6, auto,
cruise-control. Vehicle revs/surges/chuggles
200-500 rpm at highway speeds. Not all of
the time. It does it seldom under 60-degrees
ambient temp. We have replaced the fuel-
injectors, MAF sensor, and a brake-switch.
No go. We re-flashed the ECM. No go. We
replaced the torque-converter, torque-con.
clutch, pressure-control solenoid, hydraulic-
valve, shaft and sleeve. No go. Next, we
replaced the throttle-position sensor and
the ECM. No go. One tech sez maybe change
the valve-body in the trannie or replace it
all together. Another sez it could be a glitch
in the PROM. HELP!