GM has changed the part number for the radiator surge tank cap on vehicles that came from the factory with Dex-Cool. The new cap is 18 PSI (RC87 - part number 25713160), the old one for many vehicles was 15 PSI (RC75 - part number 10296465).
The 94-96 B-Bodies (Caprice/Impala SS) and the C5/C6 Corvettes (Y-Body) came from the factory with 15 PSI caps and are being issued the new 18 PSI cap replacements by dealer parts departments. Is this likely to cause any problems?
GM does a lot of strange things to save a buck. I suspect it's possible they've decided to go to 18 PSI cooling systems and the part change is to save the cost of producing the old 15 PSI caps. Can anybody confirm / deny?
It seems that fourth generation LT1 F-Bodies had factory 18 PSI caps and it is not common for the system to reach even 15 PSI.