Here you go... . courtesy of Fritz's site
8th digit Engine 1998+ 3 3. 0 Liter V6 MPI
5 5. 9 Liter V8 MPI (HD)
6 5. 9 Liter I6 24 Valve Diesel
7 5. 9 Liter I6 24 Valve HO Diesel (2001)
D 5. 9 Liter I6 Diesel
R 2. 5 Liter I4 MPI
P 3. 3 Liter V6 MPI
W 8. 0 Liter V10 MPI
X 3. 9 Liter V6 MPI
Y 5. 2 Liter V8 MPI
Z 5. 9 Liter V8 MPI (LD)
Later, Rob