Are task priorities relative?

[gds at chartertn.net (Gene Smith)]

Maybe I am (again) confused but it seems like I see different timing 
when my tasks are like this:

TaskA = prio 150  (rtem dhcp task)
TaskB = prio-150  (my app task)
TaskC = prio-151  (my Init/app task, UI1)

compared to

TaskA = prio-119  (rtems_dhcp_task)
TaskB = prio-119  (my app task)
TaskC = prio-120  (my Init/app task, UI1).

In both case I have other system tasks all at prio 100:
ntwk,ENrx,ENtx,TNTD,pty0 (seen with shell cmd "task").

I would think that since the relative priorities of TaskA, B and C are 
the same in both cases they should act exactly the same timing wise.??

dhcp is the standard rtems task. UI1 just runs in a continuous loop. 
TaskB only blocks on select() for up to 1 tick. No rtems messages or 
events are passed between the tasks.

-gene