my car loses boost at about 4500 rpm. i checked the vacuum hoses and they all appeared to be connected.
it loses boost in 1st gear at 4500 rpm then if you shift to second from first it feels like only one of the sequential turbos is kicking in, and boost guage reads 3-4. anyone have any ideas what it could be.

 

go here:

http://www.autosportracetech.com/RX-7/rx7stuff.htm

 

you have a major boost leak somewhere, check your intake piping and the couplers on the piping to the intercooler. If you know where the y-pipe is, look to the rear of where the pipe comes up where they meet, there should be an actuator there with a couple of vacuum lines there. This was the cause of my 2nd turbo to never kick in, the nipple on the actuator was rusted...

 

Check your check valves.