'65 coupe 6cyl tranny issue

'65 coupe 6cyl tranny issue

Hi everyone,

Now that the weather in Ontario is nice I have been driving my '65
coupe to work every day and I'm loving it!

Some recent engine work and carb tuning has made it enjoyable again!

Still, as the engine gets hotter and hotter the transmission begins to
slip. Slip to the point of... if I have to stop, say to fill gas or get
something at the corner store, when I restart, the car will not go
unless I shift into reverse first, then down into the lowest gear, and
then only with a little more coaxing, will it start rolling. A bit
embarrassing at the pumps to say the least.

I am hoping I am not in need of a complete rebuild.

I had thought it might be the cooling - maybe the lines are blocked or
the bottom of the rad is blocked, the fluid is not being cooled and is
becoming more viscous, hence the slip.

It's a straight six, 3 speed auto, and I have a larger '68 rad in it.

Anyone have any insights into why this is happening?

Thanks.