Searched for this specific problem but did not find anything so here goes: When tranny is cold there is no problem shifting into 3rd. As it warms the grinding starts and then when it reaches full operating temperature I can't shift into 3rd. Tried a Redline oil and that didn't help. If it was ONLY the synchro wouldn't I have trouble with 4th too. Not familiar with transmissions and wondered if it could be something else or something in combo with the synchro. Thanks for any insight on this matter.