Engine overheats

Okay so I have some experience with cars. By no means am I a mechanic but I can do plenty of DIY projects by myself.

I bought this car about a month and a half ago and the guy that sold it to me is a family friend. He told me exactly what was wrong with the car. The previous owner got into an accident. Somehow all the shift solenoids went bad and he replaced two. After I bought the car and drove it around for a little while, I noticed it overheats but not often. I replaced the airbags, airbag module, and the linear shift solenoid to finish repairing the damage from the accident. After that, the car ran like a dream.

It has been about 2 weeks and now the car cant go 5 minutes without overheating. My coolant level is perfect, I topped off all my fluids except brake fluid. I did some research and found out that the thermostat could be the problem. I bought a new thermostat and outlet gasket and went to go replace it. I opened the thermostat housing and the only piece that was in there was the top of the thermostat that rests in the outlet gasket. The rest was just gone while the old outlet gasket was melted. I removed that and replaced it and now the car wont shoot straight for hot but it will fluctuate until it gets to the "H". It still overheats and I don't know what to do. I don't have much money to experiment can someone please help.