Rear-end Gear Ratios

In a few months, I will be in the market for a new (to me) vehicle. At this point, I am thinking late model Silverado. One of the duties of this vehicle will be towing a 24' travel trailer that I acquired
this summer.
After referencing a number of towing guides, I've noticed that there is a widely varying degree of towing capacity among trucks with similarly sized engines, but different rear-end gear ratios.
My question is this: When considering a pre-owned vehicle, is there any reasonably easy way to determine a vehicle's rear-end gear ratio?
Thanks,
Mark
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Phil McCracken wrote:

Well for GM vehicles it's easy. Just look at the RPO sheet in the glove compartment. The gear ratio, brake option and tire size will all be on it. You just need to go online and grab the codes and print a reference card for you to carry. This one covers 99% of the codes. http://forums.off-road.com/gm-standard-ifs-trucks-suv-s/183040-download-gm-rpo-list-here.html
GT4    1976    2005            AXLE,REAR,3.73 RATIO GT5    1976    2005            AXLE,REAR,4.10 RATIO GU2    1976    2004            AXLE,REAR,2.73 RATIO GU4    1976    2005            AXLE,REAR,3.08 RATIO GU5    1976    2004            AXLE,REAR,3.23 RATIO GU6    1976    2005            AXLE,REAR,3.42 RATIO G80    1976    2005            AXLE,REAR,POSITRACTION G86    1990    2002            AXLE,REAR,LIMITED SLIP G90    1997    2001            AXLE REAR 3.15 RATIO HC4    1976    2003            AXLE,REAR,4.56 RATIO HC7    1976    2002            AXLE,REAR,5.13 RATIO
OR write down the VIN and have a dealer look it up.
--
Steve W.
Near Cooperstown, New York
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