I was able to eliminate most, if not all annoying high rpm shift and 5th gear cruising rattle from my gutted OEM shifter by installing an NRG Heavy Weighted Shift Knob (480g or 1.1lb). If you want even heavier, check out Shift Knobs | TWM Performance Shift Knob Store. They have 520g and 600g shift knobs but cost over $130. I got the NRG shift knob from Ebay for less than $50 including shipping. I ended up getting a SK-300BC-W Ball Black Carbon Fiber Heavy Weight Universal 1.1LBS/480g. This site has more info: https://www.getnrg.com/products/shift-knobs/feed.