Auto Transmission shifts hard going thru first gear

[JWJ]

Hi all,

My '83 MB 300D shifts hard during the first gear shift.

The colder the worse it is.

I've checked the fluid level (its good), replaced the worn vacuum valve levers, and replaced the vacuum dashpot cylinder.

The problem persists.

What other things should I look at before giving up and going to a transmission shop?

Would replacing the AT filter and fluid help?

The car has >354,000 miles on it. I don't know if its the original transmission.

JWJ