Cold TH350 not shifting into reverse

[doodah man]

Hi all,

I have a 72 with TH350 auto transmission and for the last week reverse doesn't work when I first start it up. It's been cold weather out. I can get it to go backward but only by revving the engine up and it barely goes.

All other gears work and it shifts normally going down the road. Reverse starts working after the engine temp starts to come up (usually after I've driven it about a block or so).

The fluid was a little low, so I added a pint. I haven't had a chance to check the fluid level again since adding ATF, but it's still not shifting into reverse at start up.

Any ideas what might be happening?

Thanks,
Craig.