Yes and anticipate skyrocketing boost. Watch your boost gauge and roll into the throttle in third gear.
Do this first to see if you can achieve more boost. If,after doing this,you see no more boost,wire the wastegate arm shut and see if you can produce more boost.
Have you enlarged the wastegate hole in the turbine housing?
One more thing to consider, if you have severe exhaust leaks under load, caused from cracked manifolds or a leaking 3 bolt gasket, this can affect the boost level. Sometimes you can't hear the leaks at idle, but you mentioned no leaks, so we'll move on.
Typically a standard spring actuator used with an RJC boost controller can easily control more than 21psi. A HD actuator can get on up there with the same RJC boost controller. Upwards of 30-32psi. Verify you have zero exhaust leaks, shorten the wastegate actuator arm and as was mentioned, slowly roll into the gas in 3rd gear, to see what the boost does. Make sure you have octane and are watching that boost gauge like a hawk, because if the boost spikes to 30+ and you're not "octane prepared", you could easily blow a head gasket. If octane can take whatever you give it, give it the fire hose!
(shortening the actuator rod = more boost / lengthening the actuator rod = less boost / lengthening the actuator rod to where the puck cracks open at static, IE: not running = extremely slow spool up and low boost)
It sounds like you might have a standard spring actuator. If it's easy to pull open with your hand, it's probably a standard spring. If it takes vice grips at a minimum to get it to move at all, it's more than likely a HD actuator. And the worse case scenario is this. The turbine wheel could be chewed up and or compressor wheel touching down or rubbing on the compressor cover. This can be caused from the bearings going out in the chra from oil starvation or contamination. Or from the turbo ingesting a MAF screen or one of the MAF screens' plastic rings if stock MAF sensor. Boost levels dropping with no changes and getting sluggish is a sign that the turbo is having a bad day or exhaust leaks. Just for a CYA, take the MAF pipe or hose off the compressor cover inlet and inspect the compressor wheel. Also see if it spins freely. Obviously doing this when it's cold. That's worse case scenario though. (turbo going bad) It happens.
No matter what, just be ready to lift if the boost spikes after you wire the puck shut.
Hope this helps and keep us posted.
Have you checked the alignment of the flap to the wastegate hole ? Every turbo I have installed I have had to port the hole and make sure the flap lined up with the hole . If your flap is not covering the hole completely then it would cause the same issue you are having .