1 pop under full throttle while cruising...

[dukcaln]

So I was driving the truck the other day to the muffler store to get a gasket for the leaking header and was cruising around 35 or 40mph. Well I was on a open stretch of country road, no other cars around and decided to put her through some running... so I mashed the throttle down and pop... then I backed off and mased again and she kicked down great and took off like a rocket...... my question is, could it be timing or carb adjustment.... I just replaced the plugs after getting my timimg issue solved... current set at 12-14 degrees... Only thing I can think of is carb adjustment, which I really have not takled..... any ideas...