Siemens Simos 2P / 23D / 2.3D acting weird after rechip

[grulas]

Hello everyone!
I've been doing some remapping on Simos ECUs, and only got working 2 out of 8.
A little bit about this ecu: It uses an AM27C010 OTP EPROM by default, and I replace it with SST 27SF010 Flash. I desolder the C010 with flux+hot air gun, and after I solder a socket on the board to fit the SST in. I also done versions that are directly soldered onto the board. After soldering is done, I check all the neighbouring pins for any bridges between them with multimeter continuity testing, and I also check the connection to the board via the factory test points.
My problem is dependant on temperature. When ecu is cold, everything is fine. After some time when the ecu gets a little bit warmer in the engine bay, (or for testing i heat it with some hot gun), the ECU starts sending out random stuff. The Tachometer jumping around, fuel pump relay making music, injectors and ignition also jumping around. So I think the ECU's system completely crashing.
Do somebody has any idea of where this problem can be originated from?
I have a couple of ECUs that are doing exactly the same... So weird. Is it software problem, or did I cook something? The EPROM is next to the CPU of the ecu...May it be the problem, or is it something else?
Thank you for all your answers.

[Fykus9]

I had a similar problem, which I caused myself, with the SST chip that I ordered as 5v tolerant, but from TME they supplied 3.3V and caused a couple of stabilizers, revealed by an oscilloscope.