2800 to 3000 rpms is when the turbo is supposed to be spooling up. Have you checked for any codes? Timing?
I bought a 87 22RTE truck, and I took out the motor and dropped in a 22RE. For simplicity and reliability.
Go to
http://www.22rte-trucks.com/simplemachinesforum/ and see if you can find your issue. These guys have a crapload of money in their motors alone!!
With it bogging down at those RPM's, I would say the turbo is shot. The CT20 turbo was a weak turbo to begin with.
