surging at cruise

I have a 93 Saturn sl2 that is surging <or more accurately momentarily
loosing acceleration> at while at constant speeds.

it will occur in any gear but seems to be more prominent in the lower
gears.

I have recently replaced the spark plugs, throttle position sensor,
and coolant temp sensor: and switched out the EGR valve <with another
used one> to alleviate a stalling problem at idle.
there are no engine codes being stored.

any suggestions on what might be the cause and possible solutions?

thanks for your time
kallita