Hesitation bogging under low to medium rpms?

98 GM 1500 5.7 at low to med RPM the truck tends to bog and hesitate. dose this unless i let off or give it more throttle. the motor had a light tap and cream color oil 2 years ago. i changed head gaskets,intake gaskets, replaced lifters and rods.new plugs also wires. i have put 6,000 miles on since. can't seem to figure it out. also its sporadic. dose not do it every day but most.?