1997 Chevy Suburban engine bucking during re- acceleration

My suburaban 5.7L runs fine, pleanty of power will do 90 with no problem. The problem is a bucking in the engine after I reach speed if I try to accelerate a miniman amount the engine started to buck as though there is no fuel, If I am going 50 and try to push a little to get to 55 there is a terrible bucking. as long as I am accelerating it runs smooth. If I set the cruise control at 75 it tends to smoothen out, but you can still feel minor bucking Over the last 6mo I have replaced the cap, rotor, and coil. new plugs and wires. the trans oil and filter were done 60 days ago. Truck is well maintained.