99 suburban 5.7 liter

Hey I friend of mine has this 99 suburban truck , every once in awhile it will jerk , doesn't matter if it underload or not , just cruising down the hi-way or going up hill same jerking , idles good , Evan at low speed ..taking off from a set of lights or a stop sign , I will jerk ...then for days or weeks it will run perfect ..anyone else had this prob. and found what it was ? thanks in advance ... Ps this truck does have a chip in computer ...could that cause this ? have seen one cause a stalling prob in a 97 ford ranger , removed chip and ranger never stalled again ... I would try that but this truck is 2000 miles away from me