P0700 and P0751, wont shift into high gear, shifts hard into lower ones
 

On the way into work this morning I noticed my HHR quit going into high gear, and the lower ones went into gear harder than they normally do. On the way home the MIL came on, so when I got here I pulled the codes. I got P0700 and P0751. It's a 2006 with the 2.4 and auto trans.

So, what is the most likely cause, and, what do I do to fix it. I know my reader said something about a stuck solenoid, and now I need to know where to go from here.

Sounds like a TCM (transmission control module) failure. If so, it's probably a dealer repair.

Well P0700 is a Transmission Control System Malfunction, and P0751 is stuck solenoid A Performance. Seems that you have either a valve body issue OR the TCM is crapping out as said.
I would have a reputable tranny shop at least diagnose which is the issue. The dealer is more expensive, and will want to fully replace the tranny rather than a cheaper rebuild.

Well, I have had TCM codes off and on before, so I've known this day is coming. The car has 103k miles on it, and before when things have acted wonky I've sometimes had to whack the TCM. I do have a new TCM, so I probably will give it a shot first, and if that doesn't take care of it off to the tranny shop I go!

Well, the shifting hard thing is taken care of with the new TCM, however it still will not go into high gear! When I lift the throttle it acts as if it shifts into it, but when I push it again it's like it shifts into 3rd! I don't think I've ever had as much trouble with a car as this one.

sounds like the solenoid is shot. shoulnt be to much to have it done.

I can't get a reply from the Chevy dealer on a cost estimate for that. If it is accessible by dropping the pan, then I will do that.

ImNewHere, have you contacted other General Motors dealerships to get cost information so you can compare pricing? This is a viable option to be taken.

Michelle, Chevrolet Customer Service

I am about to try some other GM dealers sicne the one I normally use has not gotten back to me for the past 3 days for a simple quote.

I finally got a response from them, saying 200 if it is a broken wire in there to 600 if it is the solenoid.