Strokergt

1991 xlt lariat 5.0L, auto with duel gas tanks (if that matters) my buddy just had motor refreshed and also transmission redone, he saud he was driving it and was running perfect and getting like 15mpg, had plenty of power. When home cut it off, went to leave again and put $20 in gas in truck, drove a short distance had to put another $20 in gas, he says maybe 20miles distance... Either way no fuel leaks, check codes and it says "safe mode"

Any thoughts???