TL;DR friendly version:
1. 3800S2 w/just over 200k on the motor ('99 GPGT).
2. Replaced the LIM gaskets myself about 5 years ago. When I did it I was a dumb/cheap-ass and did not fully flush the system, just refilled and bled.
3. Car is exhibiting the following issues: (1) Difficult to start when sitting for a while after running AND when sitting overnight on a hot day. Starts fine when the car is cold and it's cool outside (under 70f).
(2) Recently I've started loosing coolant someplace. Not 100% sure where but it doesn't seem to be hitting the ground (no wet spots). Last checked ~4 months ago and since then I've lost maybe 1-1.5 quarts tops. (overflow tank is mostly empty as well now)
4. Issue (1) has been occurring for maybe a year now. At first it wasn't too bad but has progressively gotten worse over that year.
5. Issue (2) has just come to my attention.
6. The engine oil looks OK (and always has) and, popping off the oil cap, nothing looks like that nasty white/yellow goo that would be associated with coolant in the oil.
7. No codes thrown other than one for the rear O2 sensor which has been there for ages (practically since I got the car 7 years ago).
Question: Is it possible that the remains of the dexcool crap that was in the system fouled the new LIM gaskets necessitating a replacement? The two issues combined are making me wonder as I'm not sure what else it could/would be.
Additional details (read at your own risk):
- Replaced the LIM gaskets, upper plenum, TB, and fuel injector gaskets all at the same time. New T-Stat and temp sensor and also swapped out the plastic elbows for the aluminum ones.
- "Starting Hard" = Car cranks and cranks and when it finally does fire it surges heavily once or twice before returning to normal idle. Occasionally I have to give it a little throttle right as it fires as the car does occasionally die (usually only on hot days after the car has reached NOT and then sits). IF the car does surge and die, I can crank it a second time and it usually fires right up like you would normally expect. Exhaust does smell slightly rich when this happens but that could be just because I'm cranking it and nothing's happening for a good 1-2 seconds so it's just squirting excess fuel into the cylinders.
- It should be noted that the "starting hard" issue is present in the following ways: If it is a warm-hot day (over 80f), the car will start hard even if it's been sitting overnight. If it's a cold/cool/mild day and the car has been sitting overnight or for several hours (4+) it fires right up every time.
- Also, if the car has been running for a time and then shut off you can immediately restart it and the car will start fine. If, however it is left for a bit (15+ minutes) and then started it will start hard.
- If the car was difficult to start, there is a bit of mild knocking audible from underneath (ie: you have to get down underneath the car to hear it) which goes away after about 2-3 minutes or less. It almost sounds a bit like rod knock but it's hard to be sure. It does not do this when the car starts normally/when cold.
- Rarely, if the car is put into park after driving and left to idle it will chug slightly (RPMs drop slightly and the car runs rough for about a second before returning to normal). This appears to be most common on very hot days (90f or higher ambient).
- Other than that, the car runs/drives fine and generally behaves itself perfectly.
- I've already replaced the fuel pressure regulator (twice), didn't help. MAF sensor is also new and clean. MAP sensor is also good.
- The "Low Coolant" light is on. This happened several (~4) months ago and I immediately checked/monitored the coolant level which was fine at the time. The current coolant level is still above the sensor. I'm thinking this is just the sensor that is bad/dirty but I'm throwing this in here for completeness-sake.
That should be all the details that I can think of/have checked. Appreciate any direction you guys can give me. 
