Just had the head gaskets replaced on my '01. They re-built both heads,installed new Hastings Fuel filter,new air cleaner, and now truck does not seem to have the power that it used to have. From a complete stop, I can hold it to the floor and it just takes off gently with out spinning the tires. There are no service engine lights on.
Does any one have any idea what might be the problem?

that sounds like torque management. You need to roll onto the throttle, but I would start by replacing the fuel filter again and maybe cleaning the mass air flow sensor.

The fuel filter is brand new, and I did clean the MAF as you said.I noticed this as I was driving home after I picked up the truck from the garage. I haven't even put 50 km's on in total.(The garage is closed for the weekend so I can't talk to them about this yet.) I noticed as I would leave on the green light, I seemed to have to push the accelerator pedal farther than I remember. It doesn't seem to matter if I push gently or right to the floor.
I am thinking maybe a turbo waste gate problem. They had all this stuff off of the truck while they were working on it and I am thinking that they might have something out of place.I am not sure if the waste gate is normally closed and as the pressure builds it starts to open? I am goin to tee into the actuator hose and see what pressure it has.
I am not real familiar with turbos or Duramax's in general and am having to learn real fast.
Thanks for the input, Jim

You can plug the wategate hose and not see 30 PSI on a stock tune.

Also, do you have any mods on the truck?

Please fill out a sig and tell us alittle about your truck. go to the user cp tab at the top.

More info:
I put on a boost guage, it only shows 16-17#'s of boost when you put it to the floor at 40 mph,it doesn' blow much black smoke either. When i just drive regular at 40 mph it shows no boost pressure at all. I plugged the end of the waste gate hose and it does not make any more boost. Since I just had it in the shop, it almost feels like the electronics that control the "gas pedal" isn't putting full throttle.
It just feels "REAL LAZY". I have a fuel vacuum guage between the filter and the pump and it only reads 2-3 inches of vacuum. The old filter was on for 10,000 miles and only read 4-5 inches of vacuum and I had no problems. The new filter is a Hastings brand and previuosly I had the GM filter on it. It also has a new Amsoil Air filter.

Problem solved!
It seems that over the life of my truck, the power steering hose has been gently rubbing on the aluminum charge air turbo pipe. It wore a hole in it about the size of a quarter. When they were working on my truck, the p/s hose got moved out of the way, which in turn, left the hole wide open.
Can't build boost with a hole in the tube. Got it welded up and now it makes about 21 psi.
Now I can:) again!

Wow, at least it is fixed now. Good to know. When I get back to the states, I will check mine to see the same. I just had some work done on mine about 2 months before I left.