With gears that low, smallish carb and basically stock internals you're probably looking at a 2300-2500 stall. I'd be shifting her at 5000- 5200 as long as she keep pulling at that speed. I'd give these guys a call and give them your combo and see what they say. http://www.turboaction.com/frame.html Or these guys http://www.tciauto.com/