i have a 96 3.8 5 speed in all gears if i press the gas to far down it seems like it just vibrates and chugs i replaced the motor casue the old one blew on me and it does it also to the new motor what could it be? its in all gears it does it but if i put it in neutral or hold the clutch and rev it doesnt do it its when its in gear and im driving i press the gas to far to accelerate and she just vibrates or chugs but still accelerates just not as fast as it should anyone know what it could be??? thank you

 

have u scanned for trouble codes yet? be a good start. stop by the local autozone or call and see if they can do it for ya. i would say look to the throttle position sensor and clean the egr and idle air control valve. i think the 3.8 has a iac.

 

FUEL PUMP!!!!!!! lol, ok, maybe I am just paranoid. I have heard of to many going out, and I will never forgive GM for thier grand design of "let's take a fuel pump and build a car around it"......
I would first check the Fuel Filter though.... a little bit simpler. If you get a chance maybe get a pressure check at the Fuel rail.

 

Check the things Craby mentioned.They are cheap(free is good) and easy.clean fuel filter and pressure are good things.Engines act differently under load than they do in neutral.Check your transmission mount as well since it has done this on 2 different engines.In my last 4th gen I lost the trans mount.It definately chugged and vibrated under load.most these are free checks!

 

my car did the same thing. I cleaned the egr valve and now im not having any problems. its a easy fix just get a wire brush and some solvent and you should be good to go. hopefully its not the fuel pump!

 

Plugged Cat

 

i second the egr clean that but if its bad it would trow out a code, also check you vacuum lines and maf, i did that on my 3.8 and it had it running and burning rubber again