Well me and my buddy just did a motor swap on in is truck and it has no power. its a c1500 4.3. i have looked high and low and tried every thing that has been suggested so far. i am going to check the fuel pressure tomorrow. so far we have punched out the cat and yes it was clogged. clean the egr valve it was sicking open a little bit. it just got a full tune up plugs wires, cap and rotor. i did a compression test all cylinders were at 175 psi. each thing helped a little bit but it still has no power. builds the rpm slow and it has about the power have a old 55 vw bug is a good thing to compare it to. I NEED HELP D:

 

to really check the exhaust system U need to disconnect the pipes from the exhaust manifolds and take down the road and see if it has the correct power