If it shut down while running "as if the key were turned off", the most common problem will be that the SOV closed. That can occur from loss of power to the SOV (K40 relay or more rarely, a bad SOV) or a large air leak, usually at the SOV air ring.

Neither should effect starter motor cranking speed.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)