need help i am a cad tech at cad dealer 15 yrs hava a 96 seville. starts perfect runs perfect untill drop in rev or drive loses all data lights flash radio goes out ac head blank will still run and drive limp mode. unplgged ac control module all clears up. so replaced it with salvage unit still does prob. checked all powers and grounds. run redundet grounds. but only does in gear not in park or neutral. was thinking it could be pcm losing class 2 or shorting it out ?