Replace the transmission?
 

Ok, sigh, my 2011 LT (120,000 miles) started hesitating at low speeds.Transmission runs fine at highway speeds. After driving for a while, getting up to temperature, it becomes sluggish at low speeds, jerking and threatening to stall unless you put it into Neutral at a stoplight. Recently occasional clunk when shifting back into Drive from Neutral.
During one interstate trip, it threw a CEL. I checked the codes -

P0700 – Transmission Control System - (from checking here - check for loose or damaged wires at the TCM, also a loose ground wire at the transmission ground stud. The connector to the TCM should be checked for loose or damaged pins.)

P0842 – Transmission fluid pressure sensor switch – (from checking here - could be the switch or loose wire/wiring harness issue.)

I took it into the only mechanic nearby who does transmission work who isn't the dealership. (The local Chevy dealership just changed hands and their service department never answered the phone.)

He has been swamped and finally got back to me after his diagnostic.
New transmission assembly. New TCM. Programming, fluid, alignment, and new lower control arms.
$5300 with a 3 year unlimited mileage warranty.

Thoughts?
Should I bite the bullet? See if the dealership can do better? Drive it until it breaks down on the side of the road the light it on fire and call the insurance company?

It is a well reviewed shop. I used to take my previous cars in there for work, but it was pre-HHR, so I haven't been in several years.

I’d be inclined to check at the dealership, you might be surprised! They are the ones the mechanic is purchasing the parts off of. If you don’t ask you won’t know.

I got no idea how replace the TCM got into the discussion P0700 just means to look for the cause i.e. the P0842. P0700 means the TCM is doing it's job not that it is broken. Replace or fix the pressure sensor at a transmission shop, not a fixit shop.
Replacing control arms should be 1 hour labor each plus parts (depends on where you get them) Advance has them for around $158 each.

Thanks. I dropped it off with the dealership this evening. We'll see what they say. In the morning I will upload the detailed quote from the first place.

The nearby mechanic sounds like a pirate. Run!

The P0842 could be causing the P0700.

You probably don’t really need new lower control arms, just inexpensive bushings, although sometimes the labors saved on not replacing a bushing pays for the new LCA.

Quote from first shop
Diagnostic check = $115
Transaxle Assembly (2.4L Eng - ATK - 3 year, unltd mile parts and labor warranty) = $2611
Transaxle Assembly Remove and Replace Labor = 8.5 hrs @ $115 = $978
Transmission Programming = $195
Transmission Fluid/Flush = $150
Control Arm Lower Left = $243
Control Arm Lower Right = $279
Control arm replace labor 1.8 hrs = $207
Alignment = $100
----
Subtotal = $4878
+ taxes = $476
Total = $5354

Fluid and flush a new transmission? Maybe that’s to blow out the transmission cooler in the radiator?
high prices in the LCA’s, very high.
The transaxle assembly, that include the cv axles, TCM ?

I wouldn't deal with them. The parts price is the GM retail price. Any other source (NAPA,Advance,Autozone etc) is below $200 each.
I don't know how they would assume it needs a transmission change or a TCM change based on the codes presented. Unless you asked "how much for a transmission and TCM".
Do the waive the diagnostic if you have them do work recommended? I don't get paying for a diagnostic that is part of the repair. Usually that means the plug their reader in and replace any part that is mentioned on the screen, which is not a diagnostic it is reading the codes.
I bet your local GM dealer would program a computer for 1 hour labor and they have access to the correct files.

Let’s see what your dealership says!

Well, fluid for a new trans makes sense. The flush part did confuse me. Maybe the fluid/flush is just the way it's coded in their system.
I know it includes the TCM. I don't think it included the CV joints. He said he would have to take a look at them when he got it up on the lift, but they sounded ok so he wasn't adding them in prematurely.