When I drive my car it seems to hesitate to.

When I drive my car it seems to hesitate to switch gears. It starts off fine but after it hits about 2nd-3rd gear, it seems to stay stuck at 2k rpm and it wont go any higher even if I push down on the gas petal. So I let go of the gas and pump it again to see if the rpm changes but it does not. I already got the transmission checked out and the catalytic converter and those are fine. I don't know what else it could be because my engine light is not on and I was told that since it is not on that a diagnostics test won't work. Also my car is idling even after I replaced the idle control valve.I don't know what else to do or what any of these problems can be.
Any suggestions would be a great help. Thank you!