Are you flooring it at that rpm range? Because it's low enough that the tranny should probably downshift should you be going anywhere below 40mph. Have you tried cleaning the TB? That really can solve quite a few wandering rpm issues, and is the car throwing any codes?

Might just want to grab a tuner and see if that fixes your issue, because I'm not sure if this is even a transmission issue (with the rpms sticking) or more of a computer issue? I've never had to use the O/D button to get the car to downshift, usually does that itself as long as I'm low enough in the rpm (around 3.5k is usually where my car will not downshift and leave you to go through the gear).

 

I think the OP is afraid to romp on it since he hasn't posted anything about getting on her and providing us feedback on that. Could be a Throttle Position Sensor issue... Could be a lot of things. It would help to get more info.

 

Do you think that sensor issue would throw a code nuke? Just curious, I am pretty in the dark here lol,

I agree, I think OP just hasn't gotten on the 4.0 hard enough yet. Those stock tunes are really conservative OP, if you're still running that I would suggest you get tuned soon. And you said you have a aftermarket TB?

 

I've tried getting on it, until the pedal is essentially pushed to the floor, the rev's remain pretty much steady at 1200. I do have an aftermarket throttle body on it. There's not too much information about it, I haven't gotten any error lights or check engine lights or anything. What else would you guys like to know that would help?

 

At this point I'd take it to the dealer. If you have more than one dealership nearby I'd go to each and ask to discuss this with their tranny tech and not take no for an answer. I'd be sure it's diagnosed by someone that seems to understand the problem ansd has an idea of what to check. You'll know who when you talk to him.

I'd certainly rule out a mechanical problem before I go installing aftermarket tunes unless you know for sure that the previous owner didn't screw around with a tuner and/or loaded some crap tune.