Truck is Need Help with Truck that has barely power.

[jfrank133]

About a month ago i replaced the head gaskets on my 87 chevy scottsdale, it has a 305 with fuel injection. Ever since i replaced it, my truck has no power it runs but like its barely making it, whenever i come to a stop at a light or stop sign and i give it gas to go it like wants to die. The timing is good, i checked it, double checked it and its good, also changed that EGR valve, and several emission sensors with no luck. Now i was told that it can be that i over tightend the heads, or can it be something else that i missed. I just dont know what else to check. Please help.