How many miles on the tranny??
What you describe is a symptom of a high mile gear box that is either seeing the converter leak down over night or that the seals in the clutch servos are getting hard.
TRY this
Nest time you start up cold and are ready to go, apply the brake, shift to N and rev the engine a few times to about 1200 rpm. No need to race the thing just rev for a few seconds.
Now shift to R and se if it does ok.
If things are fine then its likely that the converter is draining back over night.
You can do this trick for a long time with nothing bad happening. It allows the pump to fill the converter back up is all.
The other issue is that as the tranny gets loads of miles, the seals tend to get hard and loose there ability to hold pressure when they are cold. As the temps come up they soften and will hold.
My 94 Burb will do the same thing, but I know its issue is a converter drain back .
Give it a go and keep us posted.
Missy