What to use for RT tasks

Hello,
I am working on a project that has some realtime requirements that will
be put on an embedded machine.  After writing a few regular Linux
programs I noticed that the process was not being handled fast enough
in some instances (like maybe once or twice per thousand iterations at
a thousand iterations per second).  So I got RTLinux and thought I
would make the realtime stuff a realtime module. Well that has proven
to be a complete monster.  The realtime code needs to make some math
library calls (acos and sqrt) and it needs to be able to read from a
CAN (communication) device.  I got the math portion to work after a
while, but interfacing to the device looks be a big pain. Also this is
not the only task in the project I am in that has realtime
requirements.  And I should add much of what is already done is done in
C++ not C.
So my question is this: is using RTLinux a good idea?  Is there
something better out there?  Is there some good thorough documentation
on RTLinux, perhaps even a book to buy?  Should I just say forget it
and write everything in regular user mode Linux.
Things have just became way out of control and I am wondering if there
is something better out there.
Thanks.