Hello all , I have a 2002 GMC Sonoma 4.3l 4x4 crew cab. I have had a world of trouble with this thing. I have recently replaced the motor with a used motor i bought from a fella. The motor ran just fine in the truck it came out of it was wrecked and had a bad tranny. So i put this motor in my truck ang got it all buttoned up minus the exhaust and i fired it up just to see if all the hard work payed off and it ran fine. Well i hooked the exhaust up and the truck wont idle , it will run rough for a few seconds then dies out. so i was thinking hmm maybe the cat is clogged , so i cut it out and replaced it woth a maganaflow cat i got at advance auto. hooked it all back up and same thing running like crap with the exhaust hooked up, so i unhooked it again and it ran fine. Im stumped i cant think of anything that could be causing this issue. Im in the navy and getting ready to deploy so i need to get this thing running so i can take it to a storage unit. Any suggestions will be greatly appreciated!! Thanks in advance!