With the 4L60E, you will NOT want to tow ANYTHING in overdrive, it will be slow, and there will be minimal engine braking going downhill in 3rd, add that to the standard (weak) disc/drum brakes, small 15" passenger P-metric tires, no full-float rear axle, soft rear springs-see where I'm going here? I wouldn't tow over 3K with that setup, I'd be looking for a heavier duty truck, preferably with the full float axle, and a manual transmission.