I built my 4L60E up with the Transgo 4L60E-HD2 series C shift kit featuring Gear Command. I followed the detailed instructions and installed all the parts in the kit. I drilled the reverse input and installed the orifice plugs. I used one spacer in the 2nd gear servo. I replaced all the plastic pistons with new aluminum units throughout the tranny. I drilled alll the marked holes to .093 except the 1-2 shift which was drilled to .082. My tranny shifts nice and smooth in normal operation and really firm under hard load. Kudos to Transgo. The wire spacer in the EPC filter was used plus I drilled two 1/16" holes in the EPC screen filter per instruction to prevent filter collapse/restriction. One step demands that you make sure the isolator & converter regulator valve moves very freely in the bore. The technician I spoke with told me of the importance of making sure the valve works freely and does not bind. Adding the stronger clutch apply springs is a lot of work and a little tricky but well worth the effort.