If you must use R134A, I would switch to the parallel flow condensers and evaporators. That is the design that the late model cars designed for R134A use. If you must stick with original parts, use the refrigerant designed for the system. GM had some of the best auto HVAC systems out there, and still do.
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1976 LeMans B09 Freeway Enforcer, 455/M40 Smokey
1977 Trans Am, 400/M21 Black/Gold Bandit. 44K actual miles
2017 Sierra SLT 1500 Z71 4X4 
2019 Canyon SLT Crew 4X4 
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