5. (10 points) The sum of all four-digit numbers composed of four non-zero digits without repetition is 73326, then the largest of these four-digit numbers is $\qquad$ .
【Analysis】Let the four numbers be $a$, $b$, $c$, and $d$. According to the problem, the combinations starting with $a$ are: $a b c d, a b d c$, $a c b d, a c d b, a d b c, a d c b$, 6 in total. Then these six four-digit numbers are: $a \times 1000+b \times 100+c \times 10+d \times 1, a$ $\times 1000+b \times 100+c \times 1+d \times 10, \cdots a \times 1000+b \times 1+c \times 10+d \times 100$, the sum of these 6 numbers is $6000 a+222 b+222 c+222 d$; Similarly, the sum of the 6 four-digit numbers starting with $b$ is $222 a+6000 b+222 c+222 d$; the sum of the 6 four-digit numbers starting with $c$ is $222 a+222 b+6000 c+222 d$; the sum of the 6 four-digit numbers starting with $d$ is $222 a+222 b+222 c+6000 d$; Adding all the four-digit numbers together, we get $6666(a+b+c+d)$, then $6666(a+b+c+d)=73326$, which means $a+b+c+d=11$, so it can be analyzed that $a, b, c, d$ are one of the numbers $1, 2, 3, 5$, thus the largest four-digit number formed is 5321, and the smallest is 1235.

【Solution】Solution: Let the four numbers be $a$, $b$, $c$, and $d$. According to the problem, the combinations starting with $a$ are: $a b c d$, $a b d c, a c b d, a c d b, a d b c, a d c b$, 6 in total, then these six four-digit numbers are: $a \times 1000+b \times 100+c \times 10+d \times 1, a \times 1000+b \times 100+c \times 1+d \times 10, \cdots$ $a \times 1000+b \times 1+c \times 10+d \times 100$, the sum of these 6 numbers is $6000 a+222 b+222 c+222 d$; Similarly, the sum of the 6 four-digit numbers starting with $b$ is $222 a+6000 b+222 c+222 d$; the sum of the 6 four-digit numbers starting with $c$ is $222 a+222 b+6000 c+222 d$; the sum of the 6 four-digit numbers starting with $d$ is $222 a+222 b+222 c+6000 d$; then $6666(a+b+c+d)=73326$, which means $a+b+c+d=11$, so it can be analyzed that $a, b, c, d$ are one of the numbers $1, 2, 3, 5$,
thus the largest four-digit number formed is 5321. Therefore, the answer is: 5321.