DemonicAngel23

I have a 1997 Chevy Blazer, the motor that is in it is newer, it is a 2000 4.3 Vortec. Truck is 4x4. I recently just put this newer 2000 motor in it because my original motor blew up. The problems I am having are really frustrating to me.
I had to drop the transmission shortly after replacing the motor because the fly wheel that was on it was from the 97 motor and it wasn't the right one.


The big problems started after that.
The diagnostic machine from advanced auto parts is registering multiple random misfire, o2 sensor bank 1 sensor 3 and bank 2 sensor 1. I have purchased the two o2 sensors but am still unsure what could be causing the multiple random misfire. I have changed the plugs, and the way I changed them was to do it one at a time, unplug the wire replace the plug and put the wire back on that way I didn't get them hooked up wrong.
Someone told me that he problem with the multiple misfire could be my egr valve being out or stuck open.


I have no idea what else to do with this problem I am having, all I do know is that the egr valve is like $140 and I can not afford to replace it, and Im getting to the point where Im only getting like 5 miles to the gallon because of the way the truck is running.
I am in need of some ideas please.