I have a 98 Burb, 320,000 miles, leaking coolant like crazy, tried the GM tabs, so far no good. Original IP, water pump, transmission. Only replaced the starter, FSD, wasted gate solenoid, alternator since I bought it. My time is up, I found a new block locally, with heads, the dealer is not sure what year it is. All we have is some numbers on the block. These numbers are cast in the block, 12555506, f149, 12562492, on the head was a sticker gj 9, the old part number in his computer is 12457643, and the new number is 88894130. I am hoping someone will tell me this is a 2001 or newer block, am I correct, the best years for the 6.5 block was after 2000. I am not going to rebuild the origina block. lAny help is appreciated.