If it was a 4.7 I could answer that. We are pulling one of those now. But there are some sources of vacuum you might want to check. First, the large line from the brake booster. That one is large enough to kill it if it is loose or cracked. Should be another to the cruise control, but I cannot see that one killing the engine. Did you have someone put their foot on the brake and rev the engine in gear to check those mounts?