I have a 1996 GMC Jimmy 4x4 with a 4.3L engine about a week ago it started surging well driving at highway speeds I've changed the cap and rotor,spark plugs,Ignition wires and Fuel filter with no luck.I've taken it to a mechanic did the diagnostic checks checking egrvalve,throttle positioning sensor,maf sensor all seem to be working fine also took it to a transmission shop the only thing they could come up with is a bad 'o' ring from the torque converter not allowing the proper pressure is this possible?