I also had the 1st gear issue. The 50/50 gear oil and dexron didn't help my issue, I was going to do the 50/50 with synchromesh, but opted to drain the gear oil and use all synchro. I guess it's trial and error until you find what works. I know GL4 is the correct oil in warm/hot climates and ATF in cold per the 66 service manual. But we do what we have to.