RPM Probs. Help pls.

I have a 2004 Monte Carlo - Automatic. And when I turned the car on the rpms went to 4k and stayed there. When I went to a Drive-Thru and put the car in park, the RPM still read 4k. And, while I am driving it, it will go from 4k on upwards. Then when I got home and turned the car off the rpm guage still read 4k! I am afraid to take it up any faster in fear of red lining it. Can anyone tell me how to fix this problem?

Thanks.

Sounds like the tach is messed up. I dont think you need to worry about redlining it because instead of the needle going to 0 it zeroes on the 4 position. It sounds like from what you said that the engine isnt actually running at 4000 rpm. so at redline it probably only 2000 or so rpm. Hope im not to late with this reply. Dont know how to fix it