I don't think that kajetk1's problem has anything to do with the wastegate. He says he's pulling hills in 6th gear just fine with plenty of power, so I don't think a lack of boost is the problem (even with the wastegate plugged in and hooked up properly, just in case his happened to come undone, it still will only make it to 18-20psi or so, and is starting to open and leak boost starting at just 5 psi).

Also he doesn't have a boost gauge, and we're basing this all on two things: it's sluggish until above 2300 rpm, and he can't hear the turbo too well. He also said:
"When it is cold (like in CA it gets really cold), it is very sluggish."

but he also said:
"Than even when it is warm, it doesn't accelerate too well, till the engine goes well over 2000 RPM."

but then he also said ( ):
"Truck has good power and takes all freeway grades on the 6-th gear."

To me that seems a little strange. I don't see how the truck is pulling the freeway grades in 6th gear with good power if it's so sluggish until up near 2300 rpm. Normally we don't even suggest all these turbo fixes without any boost numbers to see if that's even an issue. I just think folks are getting off track in that direction as others have sorta hijacked the thread a bit with their own wastegate-related questions (don't mean to be a stickler but it's true )

I think the more likely suspect is the EBPV sticking shut, as the very first reply suggested. Being sluggish when it's really cold down below 2000 rpm seems like EBPV, and then doing the same even when warm... sounds like the sensor is not getting the EBPV to open when it's supposed to. But then the truck still pulls these freeway grades fine, so that still has me confused.

I do think it would be wise to check for any boost leaks first, like Scott suggested especially because of the new parts, and also may as well look and see that the wastegate actuator rod is connected. However I think that's probably the extent to which boost could be a cause of his problems, as he's pulling freeway grades fine in 6th gear with good power. Can't do that if the turbo isn't doing its job.

Still thinking we should be looking more at the ebpv or sensor. Pulling the codes with a simple scan tool would be pretty helpful, too. Anyway, guess those are a few thoughts I had...

 

The green line is for returning the boost that would be used to command the wastegate to open (via the red line) back to the intake (where the green line is inserted). Coming off the intake manifold the lines go to an electric switch, and so there's boost in this line, but until the PCM closes the switch sending boost to the actuator to open the wastegate, that switch is open and the boost is bled through the green line into the intake.

 

Thanks for additional analyze.
Some explanation - I don't know exactly what rear dif ratio my F450 has, but 2000 rpm makes it going at 51 MPH, so most of the time on the freeway I am above 2500 rpm and so far I am driving truck empty, or with couple hundreds lb on it. I check the air system for leaks and replaced one hose. No more oil stains anywhere under the hood, what I have seen before.
I would appreciate some plain English here. The search for "EBPV" brought this topic only, so I still don't know what you are talking about. Sounds like I need to install boost gauge in a hurry?

 

your truck has 4.88 gears, if it has stock size tires. 4.88's in the F-550 get me about 2000 rpm at 52mph, so its really close.

EBPV- Exhaust BackPressure Valve. its at the very outlet of the turbo, past the turbine wheel on the exhaust side. it's a butterfly valve that closes when it's cold out to create a restriction in the exhaust to keep the heat in. sometimes (rarely) this sticks closed during operation, and ive never heard of it, but it may have malfunctioned.