Look at the 8th digit of your VIN to determine which engine you have.
K = 3.7L Gas
X = 3.9L V-6 gas SMPI
N = 4.7L V-8 gas
Y = 5.2L V-8 gas SMPI
T = 5.2L V-8 compressed natural gas (MPI)
D = 5.7L V-8 gas (SMPI)
Z = 5.9L V-8 gas (SMPI) light duty
6 = 5.9L I-6 Diesel
C = 5.9L I-6 High Output Diesel
W = 8.0L V-10 gas (MPI)