'06 silverado turbo 4.8 4l80e. I can't figure out how to lower rpms while coasting. I tried a few things with the throttle cracker but nothing changes. I can disable the cracker but there has to be a better way. It feels like cruise control is on.. When I rebuilt the engine I gapped the rings, added head studs and used new factory pistons except these have valve reliefs cut into them.