Limp Mode? With no codes?!!

[pbody]

I just recently purchased a 2010 Aveo LT with 103k miles that I was told needed a head gasket... I concluded after purchasing the car that the headgasket appears to be ok. I get 220-250 compression in each cylinder, no smoke, etc.

Fixing the newly purchased Aveo:

I immediately found what the car actually needed was an alternator since it would not stay running without being attached to another cars battery. While replacing the alternator I also replaced the oil cooler, which was leaking and showing signs of oil in the reservoir (what the PO thought was the headgasket), and I replaced the thermostat for good measure.

After getting the car to run, at first, it threw a misfire p0300 code and was only running on 3 cylinders. I then replaced the plugs and noticed the coil was cracked (same cylinder it was misfiring on), so I replaced that too. Now the car starts up and idles smooth with NO more P0300!!

Excitedly I tried to drive it, but it did not come out of 2nd or 3rd gear. It has no power and the RPMs stick (the needle comes down very slow). It only goes about 1-3mph. I was able to get it back to my driveway after driving it about 10 blocks. When it sits and idles it sounds fine. Idles around 650-800. No hiccups. It sounds good.

The RPMs returning to idle slow may be some sort of indicator, or maybe just limp mode? The last time I had a slow RPM like this was on a motorcycle and it had to do with the air/ fuel ration being off. Though on the Aveo there are not codes... No lean or rich, sensor bad, etc. Nothing!

I am baffled that NO codes are being shown at all while it is limping home. How is this even possible? What could cause something so serious that the car needs to go into limp mode and not show a single codes? It must detect that everything thats detectable (sensors, MAf, etc) is ok? Would a stretched timing belt cause this? I'm not sure if that has ever been replaced.

I'm obviously confused here with a ton of questions. I do not trust the dealer to pull hidden codes for me and for what they would charge me, I can ween issues out myself and resell parts to get some of my money back if needed.

Has anyone else dealt with such a mysterious issue on this car? What was the outcome?