Normally happens after I start the car up for the first time that day but today it also happened later, albeit the car sat for about 9 hours between start ups, but for a couple minutes after starting the revs drop very slowly between shifts, then it normally goes away once I reach operating temps. I have a relatively new clutch/pressure plate/flywheel, and also all new clutch hydraulics. Could this be a throttle body or cable issue?

 

If it only happens when your car is cold it could just be normal. The thermowax on the throttle body increases the idle to about 1500 whenever cold and slowly decreases to around 750 when the car warms up. If the car cools off, you will probably notice it kick in again on startup.