Thanks for all this information.

The dealer called again this morning offering a used engine [installed] for $3500. It would only include a 100-day parts warranty. They're such a joke.

Gettin an engine in for $1500 doesn't sound bad. I'm just cautious about doing it because I would need to do the LIM replacement, and also - with 120K on the vehicle already - I could be looking at a possible trans failure soon. But its really hard to call.

For right now I'm looking at certified pre-owned vehicles. I've never had a car die like this - especially since I haven't even had it a year. I kinda want something with a warranty or guarantee from now on lol.

On a totally different note. I know the failure of the LIM could have been a cause/contributor to the rod knock [though it was fixed about 8 months ago], but how about the mixture of fuel? Its just coincidental how a rod knock occurred the day after premium and regular fuels were mixed...

I'd suggest going on ebay and doing a search for "4T65E TransGo". Buy one.
Go to your GM dealer and buy a tranmission filter. Buy 8 quarts (IIRC 8 is correct, but it could vary from car to car) of the proper transmission fluid for our cars.
Then have the mechanic that swaps your motor put the new filter and shift kit in. Use the medium firm shift and you should be golden for some time to come.
If you buy the new aluminum frame LIM gasket from GM it will only cost you around $45 and it shouldn't take the shop 1 hr to change with the motor out of the car prior to installation.

My $.02.

I had a 1992 SSEi and ran nothing but regular fuel in that car for 2 years. The engine and transmission stayed solid the 2 years i owned that car. Using regular fuel in an SSEi will not cause damage if you drive normal, i.e. not using the supercharger much, not doing any hard acceleration. You would have to use the supercharger excessively, drive fast alot, hard acceleration alot, to do damage to a motor with using only regular fuel. I drove fast alot and used the supercharger alot in my 1992 with regular fuel for 2 years and never had a single issue with my motor. It all depends on how the motor/car was taken care of before you by the previous owners. I can pretty much say that it'* just coincidental that you got rod-knock after using regular fuels. You even had them mixed, so it'* not like you were running straight regular like i did in my 1992. I'm gonna say that the type of fuel you used for a very short time had no bearing on your engine condition.

Thanks for clarity on that. I also had fuels mixed before in my old SSEi, and there was no harm done. The coincidence in this situation was just really crazy though lol.

That sounds like a decent plan, but at this point I'm leaning towards just cutting my losses and moving on. Even if I can get the car fixed for between $1500 and $2000, that'* just that much more I've put into a car that'* only depreciating in value. Between this and having to do the LIM replacement and the Pressure Control Solenoid....I've about had enough.

Thanks for all your help. I'll keep you guys posted.

Well, for the price you will get for the car as-is, you will see about $3G less vs spending $1500 on a good swap. Knowing what people largely populated area'* on the east coast will spend on a car with a bad engine you might just want to state your bottom dollar here on BC and someone from here will probably roll in with a tow-dolly if you asking too much.

Here is an example that happened just a few weeks ago with my buddy:

Buddy had a 1998 Olds minivan that had every option available that year.
120k miles but motor was blown.

Asking price: $1500 -highest offer of $700.

3 weeks with no good offers.
Spent $800 on a good engine installed by a good backyard mechanic ($400 for engine, $400 to install).

Immediately put back on market with good motor for $4200.
3 days on the market with good engine and it sold for $4000.