?RPO? codes

[mudbuggy]

Just went through the codes that are on the sticker in the glove box, didn't realize there were so many so I just took the damn thing off and brought it inside. Anyway, I ran into a couple that were not on the 'rpocodes.com' website. Would anyone have a way to source what these codes are or direct me in the general direction? They are as follows:
E6C
E92
SL1
XHB
YHB
ZHB
5X1 - this code came from a GT4 code for the rear axle ratio

Thank you Gentlemen and Ladies (If it applies)