what is my rear end ratio

IF rear differential replacement is needed - count the pinion gear teeth - then the ring gear teeth - divide pinion number into ring gear number for ‘exact’ ratio. That way if it has been replaced previously (1996) - you can purchase the exact same gear. This is especially important IF 4 wheel drive! I also see you’re having problems when backing up - that is more likely a transmission issue. Good luck!

BUT... What is my factory ratio ?

I can’t tell you that because I can’t see the *factory* production code! ... As I posted here the very first time: Look inside glove box lid for RPO (Regular Production Order) code .. Then use the link below to decipher that code: http://www.crawlpedia.com/rpo_axle_codes.htm You can also call GM dealer with last 8 digits of the vin and they can tell you ANYTHING you want to know about that particular vehicle. Good luck to ya!