A check of GMPartswiki shows the original part was GM# 3776800 (later replaced by GM# 3865358). Those GM#s cross reference to a National Seals 6818.
Although O'Rielly's web vehicle list checker says their 5778 fits your truck, a check through other source listings say it does not. A check of the PN 6818 shows they carry a Precision 6818 which shows as a match for your truck. That the one you should find will fill your need.
Note: A dimensions check between the National and Precision 6818 data shows the exact same specs for both seals.
Last edited by Gdads51; 05/09/202510:57 PM. Reason: add note
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