I have driven some 6l80 and 8l90 vehicles and can confirm I love having the extra gears. A 6l80 and a 3.42 pulls off the line harder than a 4l80 and 4.10 would but the extra overdrive gear gives u that good highway mileage. Now I will also say I’m not sure that it’s worth spending a few thousand on. If u can somehow DIY it and do it for under $2k then maybe.