I have a Sapphire hd 5770, but gpuz claims it's the flex model even though it clearly isn't. Whenever I launch msi afterburner the max oc is 960mhz because the slider wont go past that and Sapphire trixx crashs. Does the card have the wrong bios or something?
Yes you should have higher oc capability. In MSI afterburner, in settings if you scroll on bottom of "General tab" you have "Extended official overclock capability", tick that and you can overclock higher, but note, you'd need higher voltage for that, but I dont know "If you can" do anything with voltages on HD 5770.
Which power supply unit are you suing to power up this GPU ? List the PSU's model number. What does MSI AB tool say about the GPU, is it Sapphire ? What do you mean by "Flex Model" ? Click on the "Lookup" button on the GPU-Z tool. Does it take you to TPU's database ?