not sure but maybe you need the 4.8/5.3L dished flexplate with the spacer on the transmission side of the flexplate. Mount the converter to it by hand first before trying to stab the trans in. Be sure the bolt holes line up and the pilot is engaged. This is assuming you have the late model 6L with the short crankshaft, end of crank almost flush with the crankshaft seal. If the crank hangs out of the seal about 1/2" you have the 1999-2001 early style 6L and you will have to slot the bolt holes on a flat Gen3 flexplate or drill new holes.