harsh automatic shifting if lever in 3 not in D

[jeepster]

When the transmission is in D, shifts are quite smooth. But if I put in 3 (for coasting downhill),
and forget to change back later, then when accelerating, the shift from second to third is a jolt.
It has been doing this less than a month. The transmission was serviced about 6 months ago,
the fluid level is correct. My understanding is that in 3, it will not shift to higher gear, unless
the redline is reached. Would selecting 3 change anything else?

[Thomas1]

I have the very same issue, albeit I have a rebuilt/strengthened auto. I'm interested in what people have to say about it, as mine has done it since the day it was rebuilt.