[Big-Foot]

Lew - the only thing that third gear has going on in your tranny that is not shared with the other gears is the distance between the gear (3rd) and a supporting bearing. Typically the mainshaft is strong enough to take the abuse without flexing. My thinking here is that you have a defective mainshaft that is flexing too much and causing you a lot of grief. I've used and installed a numberr of these transmissions and have not seen or heard of your experience before. It is really curious.