Did the machine shop check to see if the head was warped? A head can warp a few thousandths of an inch when overheated.
Did you follow the bolt tightening sequence when torquing the head down?
Installing a head (or other engine parts) must be done carefully following the instructions in the factory service manual. A good Chilton's or other engine manual should have the same information on torquing the head bolts that the FSM has.
The FSM for a 2004 says:
"CAUTION: Engine cylinder head bolts should be reused only once. Replace the head bolts if they were used before or if they have a paint dab on the top of the bolt.
(3) With bolt No.14 held in place (tape around bolt), install the engine cylinder head over the same dowels used to locate the gasket. Remove the tape from bolt No.14.
(4) Coat the threads of stud bolt No.11 with Loctite 592 sealant, or equivalent.
(5) Tighten the engine cylinder head bolts in sequence according to the following procedure
CAUTION: During the final tightening sequence, bolt No.11 will be tightened to a lower torque than the rest of the bolts. DO NOT overtighten bolt No.11.
(a) Tighten all bolts in sequence (1 through 14) to 30 N·m (22 ft. lbs.) torque.
(b) Tighten all bolts in sequence (1 through 14) to 61 N·m (45 ft. lbs.) torque.
(c) Check all bolts to verify they are set to 61 N·m (45 ft. lbs.) torque.
(d) Tighten bolts in sequence:
² Bolts 1 through 10 to 149 N·m (110 ft. lbs.) torque.
² Bolt 11 to 135 N·m (100 ft. lbs.) torque.
² Bolts 12 through 14 to 149 N·m (110 ft. lbs.) torque.
(e) Check all bolts in sequence to verify the correct torque.
(f) If not already done, clean and mark each bolt with a dab of paint after tightening. Should you
encounter bolts which were painted in an earlier service operation, replace them."
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