Thank you Louie for your help. I will have to experiment and play with my interrupts to really understand what's going on .

I'm using a 16F1939. I found out from the melabs.com support help that a true high priority interrupt could only be achieved on the 18F's chips. That's not good for what I wanted to do, but I can find some workaround it.

The chip I'm using only has one timer, TMR1, that is 16 bits in resolution. All the other timers are only 8 bits in resolution. It would have been nice to have more than one timer with a 16 bits resolution.

Robert