Why is my RPM increasing after 1 hour of driving?

Hello!

I'm wondering if someone could provide assistance in helping me troubleshoot
the following problem I'm having with my 2011 VW Jetta SE 2.5 (~109,000
miles):

The RPM for the car jumps after driving the car continuously for more than
1:30 hrs. I notice this occurs when I take the car on long trips, when I'm driving
on the highway after 1:30 I notice the RPM will jump from 2 to 3. When I exit
the highway and break to decrease my speed, the RPM jumps to 4 then down
to 2 and then goes to 3.

When I take a 30 minute break (car turned off) and drive again the car drives
fine and then the problem occurs again after ~1:30 hrs of driving. This issue
doesn't occur when the car is running in an idle mode for 1:30hrs or more
(other mechanics can't reproduce it when the car is idle for that same amount
of time).

The engine light nor any other light comes on when this happens, also the car
doesn't jerk when this problem occurs.

I've taken it to the mechanic and have recently gotten my transmission oil
changed (problem still occurs).

Note: I bought this car in 2011 and have taken many long trips with the car
with no problem, this issue just started occurring. Also I have driven this car
stuck in traffic for ~30 minutes and this problem doesn't surface. It's not until
that ~1:30 hr mark that the issue appears.


Thank you for your help!