had the modified 87 tune on my truck since xmas day and worked great, so today i filled up from empty with 91 and decided id try the 91 tune. ...no go, said it could not install tune, pcm unlock error i believe. so i said no big deal ill put the 87 back on, and i did same setup as before. left and went up the road and the truck wouldnt come out of first gear, on its own or manual shift, it would just keep revving. so i pulled over and put my stock tune back and all is well. im gonna try an update first if that dont work ill have to call diablo i guess.