Transmission "Bump" at stop

[Starwood]

Fellas,

After I put in a new crate 350 about 3K miles ago, I've noticed something little odd with the transmission - which is a TH350 auto with the standard 3 on the tree for a 64.

It shifts fine and smooth, kick-down is perfect - but sometimes when I get to a stoplight, I feel a very slight bump - like it's "resetting" into 1st gear - after it's already dropped to 1st.

Performance is great, fluid level is good - it's just a new thang. I'm curious if this is a sign of bad things to come, torque converter related (?), or the classic "Nothing to see here...".

Any thoughts/comments appreciated - as always.