M1009 shifting hard

My 1986 M1009 shifts real hard from 1st to 2nd when it is warmed up. It shifts smooth from 1st to 2nd when it is cold. It always shifts from 1st to 2nd about 25-30mph warm or cold and 45mph from 2nd to 3rd. I already changed my vacuum lines. Why does it shift smooth when it is cold - and hard shift from 1st to 2nd when warm? Do I need to adjust the vacuum thing on the IP? Any ideas would be appreciated.
Thanks

There is a good chance you have issues internally. If things change between cold and warm it is usually a sign that a crack is opening up in the aluminum when warm. I would pull the pan and inspect everything you can closely, mostly, how much metal is in the pan when it comes off?

I adjusted the vacuum valve on the side of the IP amout 1/4" - 3/8" towards the firewall. That made all the difference in the world. About 95% of the time it shifts like a car warm or cold now. It was adjusted all the way towards the front as far as it would go before I adjusted it. Are all of these from the military adjusted like mine was? Did I hurt anything by adjusting this? It seems much much better now.

No harm. If you were towing heavy loads with a pickup, you'd want a higher shift point and firm shifts, but with a M1009, it's not really necessary. Mine shifts as yours did when cold, firm and at about the same speeds.