I just noticed this today while driving around in OD: when I get off the gas, instead of the rpms dropping smoothly, the gauge goes down a bit and about a quarter of the way down it jumps up ever so slightly. You can feel it in the car as well, it's not a big surge but it's noticeable. It doesn't constantly happen, only when i'm going I'd say 50 mph or so.

Only mods I have are in my sig. Should I be worried? Perhaps it's time for a fluid change?