GM-GMC: 2000 Chevy Engine Lack of Power, intake manifold gasket, chevy engine

Question
I have a 2000 Chev 2500 with the 5.7 liter automatic.  It seems to take a lot of energy to get this truck to move.  I also have a 1996 1500 and it takes a whole lot less to get the truck to go.  On my 2500, I hear a lot more noise under the hood and it just seems like I'm always pulling a full load.  Just before I bought it, the intake manifold gasket was changed.  Any chance the distributor was put back wrong and the timeing is retarded to much?  The other thing I was thinking about was a pluged exhaust?  Any insight into how I can check these out and what you think may be the calpret would be very much appreciated.
Thanks,
Gary

Answer
I would start with the timing.  The noise you are hearing is likely spark knock or detonation.  Not good for things.  Get a test light and set the timing, or have it looked at by a garage if you cannot.  Two ways to check for plugged exhaust, one is a back pressure gauge installed inplace of the pre-cat oxy sensor the second is to unbolt the exhaust at the manifold enough to let the engine breath and see if the performance improves.
Hope this helps