Random multiple misfire.

My 2010 Silverado has an issue with random
multiple misfire but it seems to only happen when I
put the pedal to the floor to gain speed getting on
the highway. The rpm's go up to 4,000 or so and
won't get high enough to shift unless I let off the
gas. I changed MAF, plugs, wires, and a couple O2
sensors that were bad. It doesn't misfire while
idling or when I rev it up in park. Any help would be
appreciated. Thanks.