Can you post your project or at least describe functionality of
timers and what ISR is doing in a little more depth ?
“Create Workspace Bundle”
Assuming a core clock of 80MHz, 1µs granularity / accuracy means just 80 clock cycles. Thats not much. Probably you want to use a hardware-based solution.
The jitter you see might stem from the fact that the second timer ISR has a lower priority than the first, so it can only run when the first one isn't.
Maybe you should explain a little bit more what you want to achieve.