I have picked up a 82 C-10 6.2L with a 4 speed o/d A833 manual trans and rear end code of GQ1. It has 16000 original miles verified by carfax. 1 owner and used on a farm here in Georgia. I think it has 2.73 gears in the rear end because it will not accelerate in 3rd gear on flat level road pulling a 5000lb trailer. I am trying to find out what the optimal rear end gear for towing and and good MPG would be.