Xbox 360 RROD fixed, now it instantly overheats?

I have a 2006 Xbox 360 Core Console and a 2007 Xbox 360 Elite. Both were infected with the RROD. On my Core Console, I opened it up, cleaned the old thermal paste and applied a new layer, and also applied the penny trick to my ram chips. The console works fine, but I really only used that console to practice on fixing my Elite console. I applied the same steps to my Elite console, and at first the console would not start up at all and give me instant RROD. After leaving it unplugged for about 24 hours, the console turned on normally, but then after about 5 seconds, the fans ran at highest RPM and the console shut off, resulting in the 2 Left Red Rings which indicate overheating. If anyone has experience with this issue, please help, I do not want to pay over $100 on a simple issue that should be the manufacturer's responsibility.