Did your shift kit incude something to block your low control valve? Usually a coil bound spring, or a sleeve, you can also just drop a 3/16" steel ball into the spring behind the valve body end plug reinstall the plug and pin--this is how I usually do it. If you can't put the pin back in grind a little material off the end of the valve that the spring goes on. You'll have to make the shift to second if you choose to maually shift your trans, be aware that this mod will also put the trans back to low no matter how fast your going.