Yesterday I was able to spend some time trouble shooting why my turbo hydromatic 350 was not going into reverse well. At first I thought it was the clutches slipping. However my 1st gear was strong and it uses the same clutches. My next thought was the modulator valve. So before I tried replacing it, I thought I should check for a vacuum leak or something else obvious. What I found was not a leak but a very small vacuum line and some really small fittings tying it to the secondary vacuum on the carb. So I replaced this with a 1/4 inch line from a full vacuum source and pesto it’s fixed. See the difference in the line sizes in the photo.