01 Blazer revs up

2001 Blazer, 97K miles, 4.3L, 2 door, 4x4, manual.

When I'm driving, as soon as I push the clutch in to shift gears, the RPM's go up. If I let it go without shifting, it will go up to about 3,000 RPM and stay there for about 5 seconds, and then slowly go back down. It isn't always that high or that long, but this is what it normally does. Once the RPM's go back down, it idles fine, and seems to run fine otherwise. It usually doesn't do this until I have been driving for a while. It also didnt seem to do it as much in the winter as in the summer. It does not leak anything or run hot, and my gas mileage seems normal.

also, I do not know if this is related, but I get a service engine light every now and then. I borrowed a cheap code reader from a friend, and it came up with "0122." I cant seem to find anywhere what that means.

Thanks in advance for any help!